Defense is one of the toughest areas of bridge since, unlike the declarer, your combined partnership assets are not visible. There are three guidelines that will help you tremendously on defense: second hand low, third hand high, and cover an honor with an honor. And like all guidelines, these are not set in stone and have exceptions.
Second hand low
When either dummy or declarer lead to a trick, the second hand refers to the defender who is next up. If dummy/declarer leads a small card, oftentimes, it is right to play low to this trick. The reasoning is that our honors are meant to capture the opponent’s honors. When we randomly play high second hand, we are capturing zero honors.
North (dummy): Q54
West: AT8 East: J976
South (declarer): K32
When declarer leads the 2, West (second hand) should play low. If West were to make the mistake of playing the A, it would capture zero honors and the declarer will win 2 tricks (K and Q). If West follows the advice of “second hand low” and save the A for South’s K, the declarer will win only 1 trick (the Q) and the defense will take at least 2 tricks (A and J)
Third hand high
When either defender leads to a trick, the third hand is referring to the partner of the leader. As long as you have a card that can beat second hand (either dummy or declarer) it is generally right to play your highest card as the third hand. There are definitely exceptions to this rule, but it is a good general guideline
North (dummy): 754
West: QJ32 East: K96
South (declarer): AT8
When West leads the 2 and dummy follows with the 4, East (third hand) should play the K. This way, the declarer will only take 1 trick with the A. Playing the 9 would be a mistake since declarer can win cheaply with the T.
North (dummy): 754
West: QJT98 East: A632
South (declarer): K
When West leads the Q and dummy plays low, East (third hand) should play the A. If East forgets to play third hand high, South’s singleton K will win the trick.
Cover Honor with Honor
An exception to second hand low
If declarer/dummy leads an honor and second hand has a higher honor, it is usually right to cover, since we love covering honors with honors!
North (dummy): Q65
West: JT7 East: K982
South (declarer): A43
When Dummy leads the Q, East should cover with the K. This will drive out declarer’s A and promote partner’s J and T. If E fails to cover with the K, dummy’s Q will win the trick, granting N-S one additional trick.