Explanation:
This is a safeguard measure for declarer to ensure, if she has no other entry to the long side, that she doesn’t block her access. 

Example:
An example is evident in a recent “Hand of the Week”.

East, as declarer, receives a ♥ heart lead against 3NT. She must win with the A♥ not the Q♥ to avoid blocking the suit and can then overtake the Q♥ with the K♥ in order to make four tricks in the suit rather than two. 

Such situations occur quite commonly in declarer play. Blocking the suit by ending up in the short side can also have an adverse effect by forcing declarer to prematurely use a valuable entry to the long side in order to unblock.

This relates to partnership bidding. With weak hands it is desirable to bid to the limit of the hand as quickly as possible. This makes it as disruptive as possible for the opponents who have the majority of HCPs and would prefer to have the time to reach the optimum contract for them. This is the basis for weak card pre-empts at the 2,3,4 and even 5 level which make it very difficult for the opponents to form a clear view of where they should be.

An interesting hand was played on Friday 23 rd September. On Board 19 West held
♠ 72
♥ 94
♦ 10
♣ AKQ109764

when South opened 2C (Game Force). Unfortunately, E/W are vulnerable against not but the hand is certainly worth a pre-empt of 4C because even if it only makes the 8 tricks in the club suit and goes down two doubled then North/South are very likely to have a slam on.

I would suggest a pre-empt of 5C is still a considered risk and would maximise the disruption to the opponents’ bidding. North/South can make 13 tricks in hearts their way with the aid of a finesse. West, meanwhile, can make 9 tricks in clubs. (Unfortunately the hand record for this board is not available - Web Admin).

Similarly, with a weak hand but a strong fit for partner’s opener, responder should bid immediately the full potential of her hand.

The converse is that the bidding with good hands should go slowly in order that both partners have the opportunity to describe their hands in terms of HCPs and distribution such that the optimum contract can be found. The “bottom line” is that neither partner should rush off to game, for example, in a minor if there a possibility that 3NT can be made or make a premature jump to game in any suit if a slam is possible. In order for the bidding investigation to proceed systematically to game or even slam, it is necessary for the partnership to have a clear understanding of which bids are forcing for another round, for example, reverse bids, fourth suit convention bids, new suit at three level etc.

Board 27 played on September 26 which was used as an example in the second idiom, "The one who knows goes" is also and example where taking time over the bidding reaps rewards. (Click HERE to view the Bridge Idioms and scroll to the last one to view "The one who knows goes".)
-DC

... when defending.

When declarer leads a card from her hand towards the dummy or vice versa the defender who plays next should play a low card. For example, if the K of a suit is in dummy and the defender in front of dummy holds the A it is normal for this defender to play low if declarer leads a small card towards the K. Aces are for capturing Kings not falling down in front of them.

Again there are exceptions such as “splitting honours” when holding both the K and Q as declarer leads towards the AJ or taking the A immediately in a trump contract for fear that declarer leading towards the K may have a singleton and a trick in that suit will disappear.

In contrast, (assuming declarer has not already won the trick in second position) a defender in third hand plays high to partner’s lead of a small card in the hope of either winning a trick immediately or setting one up for later. The high card played may not always be third hand’s highest card if if she takes a finesse against the dummy, for example, plays the J rather than the K when the Q is in the dummy and is not played by declarer, or third hand plays some other lower card relying on the “Rule of Eleven” (see my Lesson “Defence against NT”  click on the link to view).
 

This relates to finessing type situations where a defender plays a higher honour card (covering) when an honour card is played before her and aims to promote a card in that suit in her hand or in her partner’s hand.

For example, if declarer leads the J of a suit from her hand and the AQ of the suit are in dummy, the defender to the left of declarer covers the J with the K if she has it, in the hope of the 10 being in the defenders’ hands and being promoted. There are many other examples of when it is right to “cover and honour with an honour” in these finesse type situations.

A straightforward example can be seen in Board 26 played on September 12^th. South is playing the hand in 3NT and plays the QC from hand. West knows that her partner has very little in HCPs but may have the 10C so covers with the KC in the hope that partner’s 10C or her 9C will be promoted and win a trick.

There are also occasionally situations when it is right to duck, that is, not to cover ...

... such as when your honour card can’t be caught, or when it is patently clear that there is nothing to promote and it is better just to let declarer guess where the honour card is, and just maybe get it wrong.

Board 10 played on September 26 provides an example of this if it is played in spades by North.

Having heard very strong bidding in spades by North, West should resist covering the JS when it is led from dummy. There is no card to promote in East’s hand by covering, and by ducking the finesse cannot be repeated and West must make her KS.
-DC

This relates to misfits between your hand and your partner’s hand. 

The most common instance of this becoming a problem is where you both have six or more cards in a suit and keep outbidding your partner until you reach a level where neither suit will make.

Board 10 on Monday 26^th September was an example of this where, even with 7-1 fits, game in a major is not possible. The partnership holds 22 combined HCPs but lacks the ability to repeat finesses in the trump suit and enough control in the side suits.

Another mistake in this area that people are prone to make is taking a pre-empt out into NT when responding with a strong hand in HCPs but a singleton or void in their partner’s long suit.

This can often end in disaster when partner’s hand lacks the entries to ever set up that long suit.

Remember why it is prudent to have your partner who has opened a strong NT transfer into your long weak suit. This is because this suit may make a few tricks with its raggedy collection of trumps but may be useless as a long suit in NT.

Board 18 played on September 19 is an example. Let’s say South makes a weak jump to 2H over East’s opening bid of 1D and West passes. South should have a “high range” weak two for this bid, being vulnerable against not. With stoppers in the other suits including two possible stoppers in diamonds and a reasonable hand, North may be tempted to bid 2NT with a singleton heart only. However, hearts cannot be set up as a long suit in NT and this bid is a mistake whereas nine tricks are possible in hearts.
-DC

Clubs are for the golf course, diamonds are for your fingers ( Roberta Salob)

This simply reflects the fact that clubs and diamonds are called the minor suits because they score poorly in comparison with the major suits, spades and hearts, or a NT contract at the same level. To make game in a minor requires eleven tricks and at duplicate bridge partnerships will aim to play in 3NT if at all possible where only nine tricks are required, versus in 5C or 5D where eleven tricks are required.

Board 29, played on September 26 is an example. East/West can make 5C comfortably for a score of 600 but 4NT is also possible for a score of 630. A 3NT contract when played by East, despite having only 1 x spade and 1x heart stopper, is worth the risk at Pairs Bridge.

-DC

Get the kiddies off the street unless there is something to ruff first.

The "kiddies" are the small trumps residing in the defenders’ hands. Beginners should focus on the three most common types of trump hands (I have mentioned that there are five in my lessons and there are actually more because others can be hybrids).

"Get the kiddies off the street" means that declarer should draw trumps as soon as they get on lead so as to ensure that the defenders’ lowly trumps are not given the chance to ruff declarer’s side suit winners. The main exception is when declarer needs, before drawing trumps, to first trump cards in a weak side suit in her hand with dummy’s trumps. This requires dummy to have a shortage in that side suit (void or singleton normally).

An example is Board 13 played on September 26. North opens 1C, East overcalls 1S and ends in an ambitious contract of 4S.

South leads the 4C. East wins with the AC in dummy, plays AD and KD and trumps a diamond in dummy. Then trumps a club back to hand before trumping her last diamond with the QS. North can over-trump with the AS or not but East will make 10 tricks by trumping the diamonds in dummy before drawing trumps.

The other type of trump hand that beginners should aim to deploy is the one where either hand has a long side suit that needs to be set up. Occasionally, this can be done by trumping small cards in the long side suit with trumps in the other hand before drawing the defenders’ trumps. An example is Board 3 played on September 26, with 4S played by East.

East wins the likely QC lead with the AC in dummy, successfully finesses the JS, plays AD and trumps a diamond in dummy, plays off AS and KS and then runs the established diamond suit until North chooses to trump. East will also lose a heart trick but retains the last trump to return to her diamonds and make eleven tricks.

NB: It is very important to understand that extra tricks can only be won by trumping with trumps in a hand (either declarer’s or dummy’s) that has the same number or fewer trumps. The trumps in the hand that has greater length will win tricks in any event once trumps have been drawn. This is a common mistake by beginners. Be particularly aware of this issue when a transfer bid has resulted in the long trump residing in dummy.
-DC

This idiom relates to the bidding process to reach, hopefully, an optimum contract.

If one partner opens 1NT, for example, she has already defined her hand closely in terms of point range and distribution. Her partner is now “in the know” and “goes on” to make the contract by requiring the 1NT hand to transfer and/or describe her hand even more precisely.

In general, once one of the partner’s has defined her hand in terms of point range and distribution, the other is then in a position to determine the eventual contract.

It is a common failing that one partner, holding a “big” hand in terms of points and/or distribution, bids to a high level far too fast without first understanding fully the potential of their partner’s hand. There are clear rules around which bids and rebids are forcing and if the partnership complies with these, there is never a rush when the partnership has the benefit of the bulk of the high card points and the assurance of winning the contract.

Board 27 played on September 26 is an example where taking time over the bidding can reap rewards. West opens 1H. East has an opening bid herself and could bid 4H direct but with a doubleton spade and an extra heart in support, let’s say she bids 2D. West will rebid 2H, which shows a minimum 12-15 points for her opening but also 6 x hearts. East now knows that the partnership is likely to have 1 x heart loser at most and she, herself, has first round control in spades and diamonds. After checking for Aces or key cards, she may well believe 6H has good chances. Incidentally, a Jacoby 2NT response to the 1H opening also works well here because West will show her singleton or void diamond which makes the East hand even stronger.