When your opponent is the maker, don't lead trump.
In most cases, you are only making it easier for your opponents while emptying out your partner.
Exceptions (special thanks to Natty Bumppo):
1. The player to your left orders the ace or king.
2. You hold a singleton trump with (at least) two side aces.
3. The dealer (to your right) has picked up the right bower without being ordered ... and you hold left - ace (or even better, left - ace - x) and at least two outside aces (preferably both of the opposite color).