I try for realistic portions, but I've always had a volume control problem.

Chicken -I take whatever amount is comfortable. Prob up to 10oz
Steak/Roast- I try to limit to 8 oz. Cutting a portion of steak out to cook for next am breakfast.
Eggs two for a meal one for a snack.
Cheese and nuts-don't go there too hard to stick to a limit.
Its amazing to me that I leave food on my plate-full before I finish what I cook.