I've tried to pick a hand from our weekly online duplicate game that had interesting aspects of bidding and play. A lot of the gain in the pairs game comes from part-score battles - how high to compete, and then the battle for tricks. The bidding on this hand was fairly straightforward: playing a weak no trump East opened 1♥, South had a routine 2♦ overcall, and West had a choice between a simple raise to 2♥ or an aggressive raise to three. I think it's clear to just raise to two, with a flat hand and nine losers. Now North competes to 3♦, knowing their side has nine diamonds, and East has to decide whether to bid one more. It's fair to assume that NS have nine diamonds, but they don't know whether West has raised on three-card support, or four. They could pass and leave the decision to partner, but then West won't know whether East opened on four or five cards. 

The number of trumps held by each side is the key to how high to bid in this situation, but thankfully East doesn't need to worry. Even if West has only three-card support, so long as NS have nine diamonds (it's reasonable to assume a two-level overcall shows a six-card suit, even if it may be only five on occasion) it is right to compete to the three level. At love all at pairs it is always right to outbid the trump total by one, and bidding 3♥ over 3♦ is contracting to take nine tricks over the opponents' claim on nine tricks, so a level 18 bid (9+9=18). If there are indeed only 17 total trumps it will still be right to bid 3♥. 

Deep Finesse says that NS can take ten tricks in diamonds, and EW only seven in hearts, meaning the Law of Total Tricks is out by one on this deal. The par contract is given as 3♦+1 by NS, indicating that EW can always be held to seven tricks in a heart contract (so will get a worse score if they bid to 3♥ and are doubled, down two). However, if you look at the play in 3♥, you'll see that best defence is not easy to find. 

South led ♠A and K (king first is traditionally used to show a doubleton) and switched to ♦Q to North's ace. North gave South a spade ruff, and South exited with a diamond to East's king. After trumps were drawn this position was reached: 

East has already lost four tricks, and will have to lose at least one more. The difference between one down and two down could be worth a lot of matchpoints. How should they play clubs to give the best chance of restricting the loss to one trick? 

The obvious chance to play for is for South to hold the king. That's what East did and just led the first club towards the dummy, losing two tricks on the layout shown. However, it is better to cash the ace first and then lead to the queen. This gives the additional chance that either defender started with king-doubleton, when they would be endplayed to give a ruff-and-discard. There are other layouts that can help, too. In this case, if South plays low on the ace, East can duck in dummy when the jack shows up on the next round. South is again endplayed, as North cannot overtake without setting up the queen. 

As Deep Finesse says EW can be held to seven tricks in hearts, and no one seems to have put a foot wrong so far, there must be something NS can do to avoid the endplay. South should drop the jack under the ace. It is quite safe to do this. If East has the king, the defence don't have a club trick, so North must have that card. It all now depends on the whereabouts of the ten. If East has it, NS cannot make more than one club trick, so South must assume that card also lies in the North hand. Once this has been thought through, it is completely safe for South to ditch the jack on the first round of the suit. 

I'm not convinced this would occur to me at the table; it's all to easy just to play low automatically. I'd like to think I'd find the play of the jack on my better days. And I'm also not convinced that it's best for East to duck when South plays the jack on the second round. That all depends on the likelihood that South has chosen to play the jack from other original club holdings: KJx, KJ10 are possibilities where going up with the king cannot gain. It just shows what extra chances there are to be had when there are double-voids and trumps left in both hands. 

A similar situation arises when declarer's left with trumps in each hand and a side-suit of Jxx opposite xxx. I've often seen declarer concede three tricks without a thought, but it costs nothing to play on the suit. If one defender has any two honours doubleton (AK, AQ, KQ) they'll either have to give a ruff-and-discard or partner will overtake and set up the jack. Don't give up on these extra chances.