As shown, in all cases, West leads a spade. Dummy (North) goes down, showing a long diamond suit headed by the A, K, Q, J, ideal for enabling declarer to discard loses in other off-suit, provided they can get control.
And declarer can immediately see a problem – there are 4 potential losers (1xH, 2xC, 1xS), which means it will be essential to play diamonds before trumps, as the opposition is holding the A♥ and will take control back and exploit declarer’s losers. Ironically, E-W has control from the outset so they need to exploit their advantage before declarer can make use of the long diamond suit. So, there are two “traps” – one for N-S in that they
must play diamonds before trumps, and one for E-W, in that they need to not hand over control to declarer without first grabbing N-S’s 4 losing tricks. Two E-W teams fell into the trap mentioned, ie they followed the first spade lead with a second, handing control to declarer, who should immediately play diamonds to discard losers in clubs and spades. But, in both cases, the declarers failed to make use of the diamonds before playing trumps, and ultimately and inevitably went down one. It is no use declarer saying afterwards, “but I didn’t know West had the A♥ as a singleton” as the key observation is to realise that you will definitely go down one if you don’t play the diamonds first, so it doesn’t matter what happens by playing the diamonds as it is the ONLY way that may produce a win, if you’ve lucky enough to get early control. So, two contracts went down one because of mistakes from both teams. In the case of the 5H contract, it is interesting to note that E-W avoids giving early control to declarer by playing the A♣ on the 2nd lead, which guarantees N-S will go down. In this case, there is no mistake from either E-W or N-S. (See on RealBridge)

Play
Can East make the contract? – the computer analysis confirms East should make the contract. Why don’t you have a go using Bridge Solver Online.

West wins with the K♣ , and switches to a diamond, which South wins.

South has to lose two club tricks and the A♥. But the defence is also threatening to get a diamond ruff. If South plays trumps immediately, West will win and put East on lead in clubs. Then a diamond ruff will defeat the contract.

But, (and this is the winning strategy), South can cut the defensive East-West communications with a “loser-on-loser” play, if West has both the Q♠  and the J♠ .
South starts by leading a spade towards the dummy. If West follows low, South should not finesse the 10♠ . This might be the only way to go down if West has a hand like the above. If West has both the Q♠  and the J♠ , loser-on-loser play will still work.
After taking dummy’s top spades, North’s 10♠ is played. If East can’t cover South discards his club loser. The defence no longer has the transportation in clubs to negotiate a diamond ruff.
Set up the above hand and try the suggested solution – South will make 4H.

John and Lois was the only pair to bid no-trumps – the correct contract to be in when playing the 5-card majors system.

West leads Q♠, which is taken with the K♠ in Sth. Lead a trump, West plays the J♥ , take it with A♥ in North Don't try to draw trumps, rather lead the A♦ then the 2♦ to the K♦ in South. Lead Q♦ from South and discard one of the Clubs, then lead another diamond and discard the other club in North, which East will trump. That then leaves East with two heart winners but the contract makes!

Play:  Assuming NT is first bid by North, what is East’s best lead? East’s long suit is hearts but if East leads the A♥, he/she may struggle to regain the lead to make use of the remaining hearts. A better lead is the 8♥, (4th highest in a long suit), keeping the A♥ for later entry. North wins the first trick with the J♥. North can count 9 winners (4 spades, 2 hearts,1 diamond and 2 clubs) but must make another winner to get the overtrick. The key is the diamond suit, so North leads low to South’s long suit, winning with the A♦, then leading back the J♦. West wins that trick with the Q♦ and leads a heart back to East’s opening lead. East may or may not choose to win this trick with the A♥, it simply will not matter to the overall result. Say East ducks this lead, playing the 9♥, allowing South to win with the Q♥. If this happens, South will lead another diamond, drawing West’s K♦ and making the extra trick in diamonds. Declarer will win 10 tricks. But, if East wins by playing the A♥, and then plays a spade, it is more interesting. South must play the Q♠ then cash in his/her remaining 2 heart winners. Declarer has now won 5 tricks and has another 5 winners in North’s hand (3 spades and 2 clubs). South simply leads to North’s hand to cash in the 5 winning cards, making 10 tricks in total.

North led the 2♠.  East wins this with the A♠, creating a void in West’s hand. East leads the 5♣, winning the trick with the A♣ in West’s hand. This has now revealed to declarer that all of the missing trumps (J♣, 10♣, 9♣) are all in North’s hand. This is valuable information and can be used to good effect by declarer to ensure only one trick (a trump) is lost in the ensuing play. The key in this situation, which arises from time to time in bridge, is to leave a high trump on the left of the opposition hand holding the length in trumps and force that player into a decision about when to trump in or not by playing cards from your long suit on their left. So, in this case, the winning strategy is to lead hearts from West’s hand, putting pressure on North to decide if to trump in or not. So, declarer cashes in both the A♥ and K♥, not bothering with a finesse on the Q♥. Then declarer leads the 4♥, which North will not trump, not knowing where the Q♥ is. North plays a small diamond and East trumps in with the 6♣, with South losing the Q♥. E/W now crosses back to West cross-trumping the 9♠ with the 2♣. Then immediately plays any heart, forcing North into a position of deciding whether or not to trump in. If North does trump in, declarer will overtrump with the Q♣ in dummy, leaving North with one winning trump and one losing trump. This will be the only winner in the N/S partnership, so declarer will make 5C+1. If North doesn’t trump West’s hearts, then eventually, North will lose two of his/her trumps to E/W’s Q♣ and K♣, and North will win only 1 of the remaining trumps. This is a good example of how to take advantage of early knowledge learned that all missing tricks are in one hand. What initially looks a bit dispiriting can be used to advantage, so long as there is a long suit on the left of the opposition hand that holds the missing trumps. On the plus side for N/S, the pre-empt in spades kept E/W out of a slam. Without it, E/W would likely find the 6C small slam.

So, West must cross with a small spade to Q♠ then finesse hearts to the 10. N-S will pursue their strategy of leading another diamond, but East will regain the lead and follow-up with another heart finesse, winning with the Jack. Then West simply plays the remaining hearts and spades to make 9 tricks. This is very unusual, with the longest suit in the E-W partnership (clubs) contributing nothing to making 9 tricks in 3NT.

We stuffed up the bidding and ended up in 6 NT+1. I was dreading the score as I thought we would get a bottom board. Fortunately, most played it in 6♠ making or +1 so we didn't take a bath after all. When I looked at the bidding to see why the N/S partnerships didn't find the grand-slam I noted two things :
1. Most Norths went immediately to 4 NT (mostly Blackwood) when their partner opened 1♠. They didn't have a feel for their partner's strength and burnt up a lot of bidding room that could have been used to find out more about partner's hand.
2. Blackwood 4 NT established that they held all 4 aces but even if they had bid 5 NT (King ask), being 1 king short would have made 7♠ look risky as they could have been missing ♠ K. The take-away from this hand in my opinion is to take the time to learn the Jacoby-2 NT and Roman Key Card Blackwood conventions as they make slam contracts like this one much easier to find.

At the table I played at, South opened and was left in 1♦  making 10 tricks. Their partner thought a 2♣  opening would have been a better bid as 3 NT was on. 3 NT certainly makes on this occasion but only because the diamonds break and the ♣K is onside. 3 NT with 24HCP is a risky proposition in a matchpoint game unless you hold a solid long suit. To open 2♣ you need a hand that is just shy of game, that is 8-9 playing tricks. So in this case with 5.5 PT and a wobbly 19HCP points, 1♦  is plenty. If you have a game on you will still find it from this starting point.

Contract: 5♣ by East
Lead: ♥ A

Declarer ruffs the ♥ A in hand and leads the A♣ & K♣. The Q♣ does not fall so declarer switches to A♦, followed by K♦. The 2♦ is then lead and is picked up by North's Q♦  leaving declarer with the last two remaining diamonds. North likely returns a heart not wanting to lead away from the K♠. Declarer ruffs the heart and plays the 2 remaining diamonds, discarding spades. If South ruffs with the Q♣, they can only return a spade effectively finessing partner's K♠ or a heart allowing East to ruff then play the A♠ and then ruff the 10♠ in dummy. Declarer makes 11 tricks.

The lead from West is ♣ 10 which is ruffed in dummy with ♠ 10. Three rounds of trumps are then played followed by the top 3 diamonds. The ♣ K is discarded on the ♦Q and with the diamonds splitting 4/2 the ♦5 is then played and ruffed. The ♥ 2 is played to the ♥ J which is taken by East with the K. East plays the ♣ A which is ruffed leaving declarer with 2 heart winners and a trump for 12 tricks.

To make 10 tricks declarer needs to end play East in trumps. The technique is called "strip and end play". It means that you strip the hands down to only the suit that you want the end play in and then you give them the lead so they have to play back to you.

The successful line of play is to take the ♦A, play the ♦K discarding a club from dummy. Lead a trump towards dummy which drops the ♥K. A spade is likely returned which picks up the ♠K from East. Ruff a ♦ and return on a ♠ from dummy. Play the last winning spade, discarding a ♣  from dummy. Ruff another ♦ in dummy and lead the ♣A and K. East is now end-played in hearts. Declarer leads ♥J which East wins with the Q, but must now lead either the ♥A or 9 back to declarer who will make 1 more trick from their ♥10 & 7 combination to complete 10 tricks.

Play
The play is tricky. Initially there appears to be too many potential losers to make the 4♠ contract (2♦, at least 1 trump, and a heart). Compounding this is the fact that the partnership has a balanced hand opposite a semi-balanced hand, and often, with this distribution, 3NT is a better contract, as declarer needs to win only 9 tricks, instead of the 10 required to bring home a 4-card major. But, not in this case, as the opposition can make hay in diamonds and quickly defeat 3NT.

So let’s look at how to make 4♠. Of course, the opposition immediately leads diamonds, winning the first two rounds. Q♦ led by West, North plays the K♦, East wins with the A♦. East leads back to West’s winning J♦. Now, dummy and declarer are void in diamonds but the opposition has won two tricks. West must not lead another diamond and should realise the real possibility that this would be a bad lead, allowing N/S to discard in either hand, and ruffing in the other hand. So, West leads the Q♥, and South wins the trick with the K♥. Declarer must not lead the A♠, not knowing where the K♠ is. Declarer must rely on the K♠ being in East’s hand, and can finesse it with the J♠/10♠ combination. Of course, declarer will lose one spade, either the Q♠ or the K♠. Declarer must also not lead a heart at this point as that would leave a losing heart in the N/S combination, which would be exploited by E/W after winning a spade, resulting in declarer going down by one trick. So South correctly opts to lose the spade trick first, leading the 4♠ from South’s hand. West wins with their Q♠. West is now in a difficult position with the lead, not being able to lead diamonds or spades. Whatever West leads will give declarer the contract, but West does not know this. All declarer has to do is win the next trick, cross back to North (if required, with the A♥) and finesse the K♠, then play out the clubs, making 10 tricks.
This is a great example of identifying a winning strategy and playing to make that strategy work. Yes, assumptions have to be made, but in bridge, you will find yourself in this situation quite often. If
your winning strategy fails to win because a card wasn’t where you’d hoped it would be, then that is just too bad – you would have lost the contract in any case. Good luck with the next one.

Play
East leads the K♣, top of a run, with a touching Q♣,  South wins with the A♣. West & North discard. South plays trumps, leading the K♥. Then the Q♥, with East showing a singleton. Declarer now
knows that the remaining trumps (10♥, 7♥) are with West. Oddly enough, the winning strategy here is to play out the remaining trumps and then play the remaining tricks in a no-trumps fashion. But
this must be done carefully, as West has the potential to upset things with good honours in clubs and spades.
Declarer has an 8-card suit in spades, so leads the A♠, then the 2♠  clearing the spade threat, and having a winning Q♠ in North’s hand. But West has the lead, holds the A♣ and knows his/her partner has the Q♦. This would make 3 winning tricks for East/West but would not defeat the contract as they would end up leading back to winners in the North/South hands. It is a tricky play for declarer,
and arguably, a better contract for North/South would be 3NT, as they would need only to make 9 tricks, not 10 to be successful.
Well done to Jann and Rhonda who brought home the 4H contract, and to Suzanne and Pat who delivered on 3NT.

Play
In our Board, West led the 8♣. North takes it with the K♣, East plays the 2♣ and South the 3♣. It is always worthwhile taking a moment after the first card is led to assess the situation, and to see what tricks can be made and where there are vulnerabilities. With reasonable distribution, South can count 9 immediate winners (5 spades, 2 hearts and 2 clubs), so South only needs to make one additional trick to make the 4S contract. The simplest way would appear to be to cross trump a losing club after the A♣ and K♣ have won the first 2 rounds in that suit. Thus, South cannot just play trumps from the outset – he/she must have at least one trump in North’s hand to ruff a club. But South should be suspicious of West’s club lead, in case it is a singleton. But North/South has 6 clubs and if West only had a singleton then East would have to hold 6 clubs. Possible but the odds would favour a more even distribution. However, to be on the safe side, declarer should keep the Q♠ in North’s hand as insurance for the planned cross-trumping of clubs. On the second round, declarer should lead a small trump from dummy to see how trumps fall, so leads the 5♠. East plays the 4♠, South the A♠ and West the 7♠. Then South leads a club back to dummy’s A♣. South needs to cross back to South to be able to cross-trump the clubs, so leads the 3♥. Note: if declarer chooses to cross back by leading the 8♠, he/she will still end up making the 4S contract, but will lose a club and two diamonds. Crossing back with hearts leads to declarer making an overtrick. This is the winning strategy.

Play
At both tables, South led the 2♦. Dummy comes down, North wins with the A♦, taking the K♦  from dummy and the 6♦  from East. North does not want to lead around to dummy’s aces, so leads the Q♦ to force trumps. East plays the 7♦, South the 4♦  and dummy trumps with the 2♥.

Now it gets interesting, with many ways for E/W to lose the contract, and few ways to make it. Declarer needs to be East’s hand to lead to dummy’s strengths or cross-trump, so leads the 3♥, winning with the K♥. North is now out of trumps, South plays the 6♥.  East may be tempted to cross-trump his/her remaining diamond, but this invariably leads to going down 1. Similarly, finessing spades at this point also invariably leads to going down 1. But the most likely play would be for declarer to run another round of trumps. So East leads the J♥. With the 9♥, 8♥ combination, South covers with the Q♥, and dummy wins with the Ace.

Declarer must now play a small spade from dummy, as leading the A♠  followed by a small spade will fail as South can cross-trump a third lead of spades. It is not obvious to me how declarer can know to do this, but let’s follow the play. Dummy leads the 4♠ , North plays the K♠ , East the 3♠  and South the 5♠.

North sees the opportunity to remove the last trump from dummy by leading the J♦. East plays the 9♦, South the 5♦ and West the 7♥.
To make the contract declarer must again play a small spade from dummy and win with the JS in East’s hand. Declarer can now draw another trump, playing the 10♥, and discarding the 6♣  from Dummy. South now holds the 9♥, to East’s 4♥, but East has the lead.

East’s winning strategy is to now play the 10♣ . It does not matter if South covers with the Q♣  or not. Declarer runs the clubs until Dummy is holding the A♣, A♠ and Q♠. North has nothing useful. East has the 10♠ and the 6♠. South has two clubs and the 9♥.

It is now obvious that it does not matter what is led from dummy, the only remaining trick that declarer will lose is to South’s 9♥. But declarer will win the other two, making 10.

This board is full of traps in the 4H contract and easy to go off. But it is interesting to note that it is much easier for E/W to win 10 tricks in a 4S contract (even making an overtrick) due to the more even distribution of the missing trumps in North and South’s hand. But how East/West would ever get into a spade contract is a question for another day!

The 4♦ lead from North was won in East with the J♦, leaving plenty of entries to West's hand and cross-trumping opportunities once the trump tricks were taken. This was the play:RealBridge

It was merely a matter of a finesse of K♥  (which they did, but ended up in West's hand and missing the bottle of bubbly)!

1) p-1♦  -p-?
This is the easiest, bid 1♥. South will likely pre-empt 3♣ and West will bid 3♥. If North passes, 4 NT is an easy road to a heart slam.
2) 3♣  -X-5♣  -?
Double for penalties or try for slam? West's double shows an opening hand and support for the unbid suits and combined with East's 18HCP a small slam is likely. Bid 6♥  ?
3) 3♣  -4♦  -5♣  -?
Partner's 4♦   shows a a 6+card suit, 16+ total points and shape. Bid 6♦  .
4) 3♣  -3♦  -p-?
Bid 3♥, when partner responds 4♥, bid 4 NT ace ask.

The Losing Trick Count (LTC) can provide some assistance. A 3-level preempt can be assumed to have 6-8 losing tricks. North counts 4 losers (2 in ♠  & 2 in ♣ ) in their hand, giving a total of 10-12 losers. Taking this from 24 leaves 12-14 winners which means a slam try is worthwhile. Using the Roman Keycard Blackwood (RKCB) convention North finds the partnership is missing either an ace or the king of spades and North settles on 6♠  for the contract. On a diamond lead, Declarer wins the ♦ A and then ruffs a ♦  in dummy. Declarer successfully finesses East for the ♠K and discards the losing ♦  and ♣  on dummy's king and queen of hearts making 13 tricks for +1010