I make sure I always know exactly how much I'm going to be eating beforehand - it helps planning my meals. Even at restaurants I take a look at all my food, judge how much I can eat for my calorie allotment, then portion that off and eat only that. Portioning snacks prevents continuous munching too!
For example, I order a "burrito bowl" from Chipotle Mexican grill (leave out the tortilla!) and it's so very hard for me to stop eating since it's so delicious (but 400 cals)! But I cut it right down the middle and once I've finished one side of the bowl, I know I'm done, and it's easier to stop.