I was going to write a big detailed thing. But, I thought it would sound too authoritative and boring. So, I'll add 2 tips.

Someone else mentioned grapefruit. I recommend adding them as a snack, but be ware of eating to many acidic foods. I read a long time ago that grapefruits not only fill you up, but also seem to promote your metabolic rate.

If you're exercising, don't forget the sailors and pirates. Add spinach and oranges to your diet. Spinach and oranges seem to have a symbiotic relationship in our bodies. Eating plenty of spinach seems to act like a natural steroid and oranges seem to help your body absorb nutrients from spinach. Popeye makes sense now? As a plus, you won't get scurvy, "yar". Again, beware of eating too much acidic food.

Fun story: I once ate several oranges per day for a couple of weeks. One day I go to the bathroom and it burned when I pee. I was furious and thought my GF at the time had given me an STD. Trip to the clinic later, I find out it was just the acidic levels in my body due to eating so much citrus. Thankfully I went to the clinic before calling my girlfriend at the time.