Eat alot, may sound stupid but the worst thing you can do is starve yourself, it makes your body think its starving and so will lower your metabolism. Eat a shit load of things like potatos and pasta, nice and filling but pretty good for you. All the little things add up, instead of using butter use margerine, instead of whole milk drink semi or fully skimmed milk.

Oh and smoking really dosn't help, those munchies are so hard to resist and fruit or a sald or something just dosn't quite compare to ice cream when they hit.