When the dummy is weak and you play before the dealer, it is with
the assurance that the missing strength in the suit is over you.
This strength may be held by the dealer or by your partner. As he
is leading the suit, the chances are that the balance of strength
is with the dealer; therefore, unless you know that you can win the
trick, do not play a high card.
With ace and others in a suit, if you do not play the ace second in
hand, the dealer may win the trick and discard his worthless cards in
that suit. The second-hand play of an ace is particularly necessary
later in the hand, and when the trumps are against you.
When you play before the dealer follow the same general rules as to
covering an honour, and as to playing the lower of two honours in
sequence. If dummy holds an ace and others of a suit, and you hold
K J x play the king second hand. With small cards of a suit in dummy
and ace queen and others in your own hand, the ace should be played
second in hand.