Source: BBO 
This declarer teaching series is taken from «Learn to Play Bridge 2,» a free software you can grab from ACBL. You will also see examples from Fred Gitelman’s «Bridge Master 2000» software – you can buy the full software from Fred if interested.
The play of a hand is usually much more scientific than bidding or defense. Given a particular suit combination, there is usually one best way of handling the combination. We’ll try to teach you the logic behind the handling of simple combinations in this series; after you understand how to work out simple combinations, you will be able to apply what you’ve learned to harder ones.
10 card suits missing K:
You have a 10 card suit, and must avoid losing a trick to the King. How do you play?
- You could finesse. or…
- You could try to drop a singleton King
To figure out which is the better option, think through some likely scenarios.
Thinking process:
- 1) Suppose you lead the Queen and West follows with a small card…
- 2) Playing the Ace gains whenever East was dealt a singleton King.
- 3) Playing low gains whenever East was dealt either of 2 small singletons, or when East has a void.
- 4) Therefore, finesse is the right thing to do here.
Let’s try another one.
10 card suit missing K10x:
Go through the thinking process outlined above for this hand. EW now has K106 between them. Is a finesse, or playing the SA the right way to play this hand?
Thinking process:
- 1) Suppose you lead the Q and West follows with a small card…
- 2) Playing the Ace gains whenever East was dealt a singleton King.
- 3) Playing low still gains whenever East was dealt either 10 or 6 as singletons, or when East has a void.
- 4) Therefore, finesse is still the right thing to do here.
However, you need to be careful in how you finesse!
If West was the guy with K106, and you finesse by playing low to the J, how will you pick up both the K and 10 next? The problem can be avoided if South leads the Q on the first round, and finesse that way. Even if West were to cover, when East shows out, South will be able to return to hand in another suit, and repeat the finesse against the 10 in West’s hand.