Questioneer2 is half way there. Eat smaller portions so that you fool your brain that you're eating more. Then, when you finish the portion you intended to eat, walk away from the table. You may feel for a few minutes that you want more to eat but after a day or two you'll find that it no longer troubles you.
I once saw a guy at work doing mini push-ups, sitting in his chair at the lunch table with his hands on the table edge. When I asked what he was doing he said that a doctor on TV had said that the best exercise for weight loss was "pushing yourself away from the table". And, yes, it's a true story. The guy was pretty thick.