Don't hurry when exacting a penalty.
Don't think entirely of your own hand.
Don't take advantage of your partner's breach of etiquette.
Don't think that bad play won't sometimes win tricks.
Don't forget the score for an instant.
Don't ignore the value of small cards.
Don't fail to see your partner's first discard.
Don't be deceived by the dealer's play.
RULES
It is impossible to suggest rules that will cover the play of every hand. Rules are formulated after the analysis of a great many hands, and are therefore made to meet the usual distribution of the cards. When the fall of the cards reveals an unusual situation, unusual means must be adopted to meet it; and here your reason and common sense must come to your aid.