Source: http://kwbridge.com/counting.htm Ever wonder why good bridge players seem to be able to see through the backs of your cards? Why they are so successful in finding the right lead, locating missing honors, guessing the distribution of their opponents’ cards? The answer is that they are usually not guessing. Whether they’re defending or declaring, good players are constantly gathering clues from the bidding and play and using them to make logical assumptions about the location of the unseen cards. This exercise – some call it a talent — is often called card reading, and it’s a skill that even beginners can develop. It involves determining the overall layout – the length and strength (honor holdings) of each suit in each of the two hidden hands. The first and most important step in card reading is counting the hand, which focuses on figuring out how many cards each player holds in each suit.
Counting two or more suits Once you master counting one suit, you’ll want to move on to figuring the distribution of two or more suits. To do this successfully, you need:
• The ability to count to 13 at least twice (4 times, if possible).
• Memory skills, which can be developed with practice. (See Developing your Card Sense for tips on developing your bridge memory.)
• A basic knowledge of the meanings of bids, leads and defensive signals.
• Technical skills – knowing how to use “discovery plays” and other techniques that help you collect clues about each player’s distribution.
• Concentration. You have to put some energy into counting. Pay attention to every trick and modify your picture of the unseen hands as you collect new clues.

Collecting information From the bidding:  Whether you’re defending or declaring, use what you know from the bidding to come up with an initial picture or one or both opponents’ hands. You can start with very simple assumptions, such as the minimum length promised by an opening bid or response. If an opponent opens 1H, for example, you can “see” at least five of his 13 cards. If that opponent makes subsequent bids in the auction, you’ll learn more about his other 8 cards and you can often build a fairly accurate — or sometimes perfect — picture of his hand pattern. You can also use the bidding to determine what a player does not hold in a suit, which will lead you to conclusions about his length in other suits and, in some cases, his partner’s length in a suit. For example:
• If an opponent opens 1D and then does not support his partner’s major-suit response, it’s guaranteed that opener has 4+ diamonds (because the only time he would open 1D with a 3-card diamond suit is when his distribution is exactly 4-4-3-2).
• If the opponents’ auction goes 1H-1S-1NT, you’ll be able to narrow down your picture of opener’s hand to one of three patterns: 2-5-3-3 or 3-5-3-2 or 3-5-2-3. This conclusion is based on three logical assumptions: (1)  Opener showed a balanced hand with his 1NT rebid, but he did not raise his partner’s 1S response (so he has exactly 2 or 3 spades); (2)  He did not rebid his heart suit (so he holds exactly 5 hearts); and (3)  He did not show a second 4+-card suit (so he has at most 3 cards in each minor).
General tips for counting:
• Memorize the common patterns of the 13 cards in a suit — 4432,  4333,  4441,  5332,  5431,  6322,  7321, etc. (Note that all the patterns of four numbers fall into one of two even-odd combinations: three even numbers and one odd, or three odds and one even.) Drill yourself on the patterns and become so familiar with them that you won’t even have to think once you get a partial count. If you discover that each opponent has 4 cards in a suit and you hold 2 cards, you won’t need to do any arithmetic to know that partner holds 3. The 4432 pattern will instantly pop into your head.
• Concentrate on how the unseen cards divide. Once you become adept at recognizing the common patterns, start thinking not just about the number of outstanding cards in a suit, but about how they might break. If your hand and dummy have 8 total cards in a suit, try to focus on the possible divisions of the 5 missing cards. With practice, it will become second nature for you to go beyond thinking “5” and start thinking “3-2,  4-1,  5-0″.
• Memorize the original layout.  Whether you’re declaring or defending, study the dummy at trick one and create a mental picture of its distribution. Commit it to memory by repeating the pattern in your head (for example: 3-5-3-2, or 35-32). Do the same with your own hand. Later in the play, if you can’t remember how many cards have been played in a suit, you can often reconstruct the play — and figure out how many times the suit has been led — by recalling your mental picture of the number of cards you and dummy originally held in the suit.
• Mentally review the bidding before you play to the first trick. If possible, come up with a picture of each player’s general hand pattern and high-card strength. Consider not just what the hidden hands actually bid, but what they did not bid.
• Focus your count on just one unseen hand.  The easiest hand to count will usually be the player who made the most bids during the auction, or who made the opening lead. Use what you know about that hand to figure the distribution of the other hidden hand.
• Consider the skill of your opponents. The more experienced they are, the more reliable their bidding and carding will be … and the easier it will be for you to make accurate assumptions about their hands. Popular bridge author Eddie Kantar observed, “A madman’s hand is particularly hard to count, but he’s usually in the wrong contract, which evens things out.”
• Practice, practice, practice.  It will take time and lots of practice before you can process all the information available and make the right conclusions. You can speed your progress by making a concentrated effort to count at least one or two suits on every deal you play, even on those where it appears you can’t affect the result. The more hands you play and the more suits you count, the more adept your brain will become at remembering the cards.
• But … don’t overload your neurons.  Early in the play, try to decide which suits are critical and concentrate on counting just those suits. If you’re declarer, your count will usually be focused on your longer fits — the one or two suits where you and dummy have the most cards. If you’re a defender, try to start your count with the suit you or partner led, then move on to figuring the distribution of one of the declaring side’s longer fits.
Tips for declarers:
• Study the opening lead.  Try to make some conclusions about the opening lead. Does the card led suggest length or shortness in the suit?  Does it pinpoint the leader’s exact length  (and therefore his partner’s length)?  Does it show an honor combination or the lack of one?  What does it tell you about the leader’s possible length or honor holdings in other suits?
• Play on one suit at a time. Once you begin drawing trumps or establishing a suit, stick with that suit. If you have to lose a trick, resume leading and counting the critical suit as soon as soon as you regain the lead. Resist the temptation to cash high cards in other suits unless you have a clear purpose in doing so (you need them for entries, for example). When you’re done cashing tricks in the first suit you’re counting, move on to the next suit and start a new count.
• Watch the defenders’ count and attitude signals. Be aware, however, that you can’t trust these implicitly. If an opponent thinks a signal will be of more help to you than to his partner, he may not give an accurate signal, especially late in the play.
• If possible, delay your important decisions. Collect all the information you can about the defenders’ distributions before you decide how to attack a critical suit. Run your long suit or cash a few extra trumps (if you can do so safely) and see what you can learn from the opponents’ discards. Use discovery plays to get a count on side suits. If you have tricks to lose, consider giving the defenders the lead to see if they’ll provide you with a discovery play.
• Play the odds.  If, for example, you have a two-way guess for the location of a queen, use your count in the suit to decide which way to finesse. If you determine from the bidding or play that one opponent is likely to have more length in the suit, finesse that opponent for the missing queen. (See “At the Table” below for an example of this situation.)
Tips for defenders:
• Watch partner’s signals. They tell you about his length and possible high-card holdings in key suits.
• Give partner good signals so he can count out the hand, too. Use your judgment here, though. Some signals help declarer more than they help your partner, so it’s sometimes right to withhold a count signal if you think it will tell declarer how to play a suit.