My son's got it all figured out:
1) Run everywhere. No walking allowed.
2) If you're not running, be jumping. Up curbs, down from curbs, over painted lines...
3) Gag at supersweet foods like cake icing and cokes.
4) Eat only when you are hungry. Don't slow down at noon just because it's noon. In fact, pay no attention to what time it is.
5) Don't eat just because someone hands you food.
6) Don't eat just because something's left on your plate.
7) Eat snacks like 5 crackers, a tiny box of raisins, or one piece of cheese to tide over until you're really hungry. (Not until a certain time--but until you really really want to eat.)
8) If you're not hungry, say in a really loud voice "I'm not hungry!"
9) Drink tons of water.
10) Spend very little time hanging out in the kitchen.