1 Never, but never forget you are playing with a partner.  It pays to consider what things may look like from partner’s point of view, particularly when you are privy to information that partner isn’t.
2 You cannot defend properly unless you remember the bidding.
3 You cannot defend properly unless you know what system the opponents are playing.
4 You cannot defend properly unless you watch the cards, particularly the little fellows.
5 You cannot defend properly unless you count.
6 You cannot expect your partner to defend properly if you make faces or show other signs of disapproval.
7 Keep one goal in mind: DEFEATING THE CONTRACT.  Do not worry about overtricks unless you are defending a doubled contract or are playing tournament bridge.
8 A player who hesitates during the bidding is likely to have a problem hand. Keep the hesitation in mind.
9 The figure to focus on during the defense is the number of tricks you need at any given moment to defeat the contract.  Defense is based on this figure.
10 Give your opening lead a little consideration.  The fate of many a contract is determined by that one card. Use the bidding as a guide.
11 Make sure you and your partner are on the same wave length concerning leads and signaling conventions.
12 Don’t compound a crime.  If you, or more likely partner, has made an error, do not lose your cool. Many contracts can still be beaten after one defensive error, seldom after TWO.
13 If partner makes a nice play, a kind word or two at the end of the hand goes a long way.
14 The speed of the play, may be a clue to declarer’s problem. When playing a 4-3 trump fit, play usually slows to a crawl.
15 When two possible defenses present themselves to defeat a contract, both equally likely, select the simpler.  (Unless you are looking to make an appearance in a newspaper column.)
16 If you can see the winning defense, take charge.  Don’t put additional pressure on partner if you don’t have to.
17 Keep partner’s skill level in mind.  Lead a weaker player by the hand.
18 Watch partner’s spot card signals.  The stronger your partner, the more meaningful they are.
19 Keep your singletons and doubletons in the middle of your hand.  Some players watch where your cards come from.
20 Try not to guard against non-existent or highly unlikely dangers; guard only against those that are consistent with the bidding and play.
21 As declarer, being able to take a trick with one of two equal cards, take the trick with the higher equal.  The exception is at notrump when you have an AK stopper. If you plan to take the trick, take it with the king.  Taking the first trick with the ace is very suspicious. If that were your only stopper, why didn’t you hold up?
22 As declarer when leading a suit that has equal honors, lead the higher or the highest if you want it covered, lead the second highest if you don’t want it covered. It works like a charm.
23 As declarer, play cards you are known to hold If it cannot cost you a trick. For example, if a queen is led, dummy has small cards, you have KJ doubletonand the ace is played on your right, play the king. NOT the jack. Third hand knows you have the king from the lead of the queen, and the opening leader knows you have the king from partner’s play of the ace. Since the king and jack are equals, and since they both know you have the king, PLAY IT!  PLAY IT!
24 Defend passively if side suit tricks cannot get away; defend aggressively if they can. Reread this tip!
25 Be on the lookout to double artificial bids (Stayman, Jacoby Transfers, cuebids, Blackwood responses) to help partner out on opening lead. However, low level doubles of artificial bids require both length and strength (typically five or six card length with 3+ honor cards in the suit). The higher the level of the artificial bid, the shorter your length must be-but you still must have honor strength in the suit (KQx, for example).
26 As declarer, assuming the opponents are playing standard leads and standard signaling, concealing cards lower than the one that has been led or lower than the one played by your RHO confuses the count plus the meaning of the signal.
27 The bidding is the key to defensive strategy and to a great extent influences the play of the hand. Treat the bidding as you would a best friend.
28 If you and partner lead Ace from Ace-King be forewarned that it is a trick one strategy only.  After trick one the king is led from ace-king combinations. Also, the king is led from the ace-king in any supported suit or in any suit partner has bid, supported or not. It is also led when defending contracts at the five level or higher. The reason for this is that the ace is often led without the king at such a high level.
29 When signaling encouragement with equal spot cards, signal with the higher equal. With A987, signal with the 9. If you signal with the 8, you deny the nine!
30 Take your time before playing third hand to the first trick. It is often times the most important play you will make in the entire hand.