TH asked: When you are declarer in a suit contract, you count your losers, then work out a plan to achieve your contract. (In a no-trump contract, you count your winners.) What is the best way to count your losers? Is there a quick way to do this? Or is it just practice?
When you are planning your hands as declarer you can be fairly precise as you can look at both dummy's and declarer's holdings.
Holding Qx opposite KJx would be 1 loser, Ax opposite Kxx would be no losers provided you have trumps to ruff with. You can also take into account information that the opponent bids or opening lead. Sometimes of course plans go awry, such as when there is unknown extreme distribution in the opponent hands and you suffer an unexpected ruff, but on the whole this planning is an important and very useful part of declarer play.
During the bidding there is also a standard way to estimate your losers once you have found a trump fit. For the first 3 cards on every suit count one loser for each trick you would lose if the suit were played from the top. So an A singleton, any void and AKQ would be no losers, Ax and Kx would be 1 loser, Qx and Qxx would both be 2 and JTx would be 3. Don't count any cards beyond the first three in any suit as losers. This is a rough approximation but generally quite good.
There is also a fairly accurate way of estimating your partner's loser count from the points that their bidding shows. A minimum opening hand (13-15) typically shows a 7 loser hand. This is adjusted with one loser less for every extra three points shown and one loser more for every three points less shown. So a medium opening hand (16-18) would typically have 6 losers, a maximum opening hand (19-21) 5 losers, and a game force opening hand (22+) 4 or less losers. On the other more common side side a minimum response (6-9/10) would typically have 9 losers while a medium (10/11-12) response would suggest 8 losers.
What can you do with this information? Add your and your partner's loser count together and subtract the total from 24 to estimate the partnership's loser count. When you have a very distributional hand with an agreed trump fit, this is sometimes a better estimate of trick-taking potential than relying solely on points to value your hand.