Here are two hands you hold from two different auctions. You are on lead in each hand. What do you lead?
Here's the auction for Hand 1:
S W N E
1N P 3N P
Here's the auction for Hand 2:
S W N E
P 1D P
1S P 1N P
3N P P P
These are two hands played by my partner or me recently. In the first, I eschewed the heart 5 lead. While it's true we might get lucky and my partner might have the Ace, King, or Queen of Hearts, and opponents might not be able to run nine tricks before I set up the Hearts, that's a long shot. The best lead here is the Ace and King of Diamonds and a low diamond. In the actual hand, my partner had Queen fifth of diamonds, we took the first five tricks and were the only pair to set the contract.
In the second, my partner led a Club and opponents ran off 11 tricks before my partner got her Ace and King of Hearts. Here, as in Hand 1, the lead should be the Ace and King of Hearts and the low Heart. In the actual hand, I held the Queen, Jack, and three hearts and we would take the first five tricks. Here's the actual hand:
I gave this problem to many people at all levels. None chose the winning lead of the Ace and the King followed by the remaining card in the suit.
Whenever you find yourself on lead defending 3 No Trump and you hold AKx with nothing else in your hand to try to set up and your partner hasn't bid, you should lead out the Ace and King and the little card. This has three desirable effects. First, you get two tricks you might not get if opponents can run the other suits, which is likely. Second, you might catch partner with the Queen and more cards in the suit, especially if it's an unbid suit, a fit you'll never find if you don't make the right opening lead. Third, if partner has 5 small cards in the suit, you will set up two tricks for her if she ever gets in by getting rid of all the other cards in the suit with your three leads.
If you lead the small card, you block the suit for your partner if you get in and win your Ace and King; you can't get back to her. While this should be obvious, if your partner has actually bid the suit, your leading the Ace, King, little will unblock the suit for her.