My rule of thumb is "put one of everything you wanna eat on your plate" like, one spoon full (not tablespoon but yanno, serving spoon long as its not outrageous), and if you finish, you finish. If you don't, yay. If you want more, pick the lowest calorie/fat food (generally the turkey, sometimes).
I'm not a big pie person and a "full meal" like Thanksgiving, I can eat less but feel more full since its all heavy food.