It's been my experience that the biggest downfall to dieting is depriving myself of foods I love. It's amazing that when I realize I can't have a certain food, I seem to want it even more, and I obsess over NOT being able to have it! Here's the trick...let yourself have a small splurge everyday.
Allow yourself one treat, whether it's a piece of chocolate or a small order of fries or whatever your Achilles Heel might be. Knowing that you can have one treat per day keeps you from feeling deprived and helps you to keep on track the rest of the day. You know it won't be the end of the world because you can have a small treat again tomorrow! If you deprive yourself, you tend to overdo it when you finally have a taste of the foods you love so much (that don't necessarily love you back). Everything in moderation, right?
Be mindful of serving sizes and make sure you counteract your treat with the appropriate amount of exercise to balance out. Better to have a small treat everyday than to go all out and REALLY set yourself back by overindulging! Think of it this way, it's easier to work off 2 pieces of chocolate than to try to work off a whole box because you've felt deprived!