Surely a player of your bridge skills is familiar with most or all of the following tips you are about to read. But is your partner?
Fact 45:
If the opponents are playing standard signals, this tip is sure to screw them up.
Say the 3 is led against notrump and dummy has the A-K-5 and you have the Q-6-2. You play the king from dummy and third hand plays the 4. If you play the 6, concealing the deuce, consider the confusion you have caused: fourth hand won't know if partner has led from a four- or five-card suit (can't see the deuce) and the opening leader won't know if partner is signaling with something like Q-4-2. (can't see the deuce).
If you play the deuce at trick one, East knows that West has led from a four-card suit and West knows that partner's 4 is discouraging. For shame.