When you're eating, only eat one helping, or serving--one plateful. No matter how good it is, tell yourself from the start, you're not going back for more. You may not have the will or strength to do this--so start by asking God for help before you begin eating.
It may help you to slow the eating process down. Eat very slowly, chewing each and every bite. Really savor and enjoy the food you have. Be totally conscious of this sacred act of receiving the blessing of food and sustenance.
Think about how you're feeling while you eat, not just about filling your stomach. Are you at peace, or is there some worry or stress eating at you? Take a slow deep breath between bites, feel some gratitude, and make this a peaceful, nurturing time.
Most importantly, while you're eating when you feel the slightest full feeling--stop, say a prayer, ask for the power to stop--then get up from the table, go somewhere else, do something different.
If you finish a meal and still feel hungry, wait 20 minutes. It takes that long for your stomach to tell your brain that you're full. While you're waiting, have a big glass of water.