If it has a TV commercial, don't eat it!
Buy food that you don't like. Not that you HATE, but stuff that you don't enjoy eating.
NO SALT. Bland food is less enticing.
Drink lots of water.
Eat small meals several times a day, not big ones at night.
Get into the habit of CHEWING, and finish chewing then swallow before you reach for the next bite. This slows down your eating and lets your stomach catch up.
Only eat when you are HUNGRY. Stop eating as soon as you are no longer hungry, even though you will waste food. It's already food that you don't like, so you won't miss it, and it's cheaper to throw that away than to pay for your first heart attack.