With such combinations as K x x x, Dummy having Q x, the suit should not be led.
When you have a suit which is both long and strong, such as A K x x x, and Dummy has no honour in the suit, it is a common artifice to underplay, by beginning with the smallest, if playing against no-trumps and you have a card of re-entry. This should not be done unless you have the general strength to justify such a finesse.
If you open a long suit, Dummy having only small cards, and your partner wins with Q, J, or 10, and does not return it, he has evidently a finesse in the suit and wants it led again.
End Games. In the end game there are several variations which are made possible by the fact that the cards on your right are exposed.
With A J x, Dummy having Q x x, the small card should be led.
With Q x, and an odd card, Dummy having K x x of the first suit; it is better to play the odd card; but if for any reason this should not be done, lead the Q, hoping to find A 10 with your partner.
The state of the score must be a constant guide in all end games. For instance: You hold Q 10 x, Dummy having J 9 x. If you want only one trick, play the Queen; but if you want two, play the small card.
SECOND HAND PLAY. The easiest position to play as second hand, is, of course, with the Dummy on your left, because Dummy’s cards will show what is best to be done. If a small card is led, you having King, put it on if Dummy has not the Ace; unless you want partner to get the lead. If Dummy has only two cards of the suit, neither of them the Ace, always play your King.
When the declarer leads a suit it is often important to count how many he and your partner can possibly hold. For instance: You have four, K x x x; Dummy has four, A J 10 x, and declarer leads the Queen. It is useless to play your King; for either the Queen is a singleton, and the declarer cannot continue the suit, which will compel Dummy to lead it to you eventually; or, the third round will be trumped, perhaps by your partner. If you have only two small cards with the King, put it on the Queen. You cannot save it, but you may establish your partner’s 9.
In the last three tricks, if you find yourself with a doubtful card, and the best and a small card of a suit which the declarer leads through you, win the trick and lead the doubtful card, for if the declarer held the best of that suit he would have led it first, to be sure of a trick.