[MattieShoe]

Another rule of thumb is to lead through strength to weakness... Basically, the person playing fourth is in the best position. If you lead a suit that you know the declarer (playing fourth) is strong in, you will often end up finessing your partner. So if the (future) dummy bid hearts and his partner didn't support them, then the partner is likely weak in hearts. The dummy COULD have KJ and your partner might be sitting behind him with AQ. Or dummy may have AQ and partner is sitting behind him with the KJ, and so on.

Leading an ace in a suit your partner bid is not bad -- it lets him know where the ace is and isn't going to finesse him, and likely isn't going to help your opponents in setting up a long suit.