Save at least one card of your partner's long suit, unless you are forced to give it up in order to protect your hand.
After you have led or shown your suit your discard should be from weakness.
If your partner is discarding from weakness, protect the suit that he is throwing away, if you can.
If forced to protect honours in other suits, don't be afraid to unguard honours in the suit in which partner is strong.
NON-DEALER'S PLAY
Second Hand
In determining the card to play second in hand, you will find it a great assistance to ask yourself why the dealer is leading that suit. You can usually infer from the dummy's cards and your own hand what the dealer must hold to have led the suit.
Cover an honour with an honour. This should always be done holding a perfect or an imperfect fourchette (a card higher and a card lower than the one led). An honour should be covered when by so doing you hope to make a card good in your partner's hand. Don't cover holding a K, Q, or J three times guarded, unless your next best card is a nine or better.
Don't hesitate. By hesitation a player often shows the dealer how to play his cards. Play quickly, and if there is any doubt as to your play, play the lowest card you hold.
If the dummy has a tenace over your cards or can take any card you hold, play low; let the dealer do the guessing.