Take time to watch yourself eat. Write down everything you eat for a few days, or a week or two. While you're at it, note when you ate, where you ate, what you were doing, and how you felt when you ate.
After a few days of observation, what do you see? Do you always eat donuts on the way to work? Do you think that's good for you? Did you always have dessert after every meal? Is every meal a three course (or more) extravaganza? Do you have a candy binge every day between 4 and 5 p.m.?
Now, go back to analyze your logs and counsel yourself. Give yourself the kind of best advice you would give to a friend.