Dummy on the Right. When Dummy leads through you, your skill in avoiding any traps the declarer may be setting for you will depend on your knowledge of how he manages his hand, and your ability to infer what he holds.
As a general principle, it may be assumed that any high card led by Dummy forms part of a combination, the unseen part of which is in the declarer’s hand. If Dummy leads a Queen from Q x x, you holding A J x, it is almost a certainty that the declarer holds the King. If you have A K x, the dealer must have J 10 and several others. If you have K x x, the declarer probably holds Ace, or a long suit headed by J 10.
When Dummy leads strengthening cards, they must be to give the declarer a finesse. If he leads a small card from small cards, some high-card combination must be in the declarer’s hand. In such cases it is useless for you to finesse. If you have any sequence superior to the card led, cover with the lowest. There should be no false-carding in this, because your partner is the only one that can be deceived.
With A K and others, play the King, whatever Dummy leads.
With A Q and others, Dummy having nothing higher than the 9, play the Ace.
With K Q 10, play the Queen on a small card led, unless Dummy has the Jack.
With A J 10 x, play Ace if Dummy has no honour in the suit. But if Dummy leads the 9, cover with the 10; if it loses, you lie tenace over the declarer.
With A J x, play the Jack on a 9 led. This prevents the finesse of the 9, and retains command of the suit. If Dummy has both K and Q, play your Ace. It is useless to play the Bath coup, for the declarer knows your cards, and your partner only is deceived.
With K x x, if Dummy has not the Ace, do not play the King, no matter what is led.
With Q x x, unless Dummy has both A and K, do not play the Queen. If your partner has the Jack guarded, one of you must make a trick. If Dummy has A J, and leads J, put on the Queen; it may make the 9 or 10 good in your partner’s hand.