So, the best tip I've ever heard about sustaining a diet is to not put yourself in the position to eat bad foods in the first place. In most situations, people have bad foods like chips, candy, and other snackfood in the house, leaving them always tempted to snack. This is a losing proposition. Like gravity, if you have these foods in the house, they will get eaten. Whether its today or tomorrow or next week, you will eventually break down and eat them.
The trick is to not have the items in the house in the first place. When you're shopping at the supermarket - go when you aren't hungry so you're in the best emotional state to make decisions for your body. Going to the grocery store hungry is a quick way to end up with all types of food you won't eat!
I used to be a candy freak. I'd eat it all day. Sometime during college I realized I just stopped having it around (though I still love it). My cravings for candy have been severely reduced simply because I don't keep it around. On the contrary, my parents still eat candy bars etc. every hour because they leave these treats in bowls all over the house. These little bowls are just "asking" for you to take a nibble as you walk by. Keep that stuff away! Out of sight, out of mind. Better yet - out of house.
My advice is to not approach the dieting problem like you can will your way through it. Make it easier on yourself. Play games with your mind. Use the above tricks to take candy and snacking off your mind for good. You have nothing to lose - just try it out for a while. I bet you'll be surprised how easy and effective this can be.