I was lucky enough to have a very good personal trainer at work for about 5 months, and he revealed the most startling fact for weight loss:
Eat less and exercise more!
I'm not trying to be a wise-guy; it actually works. The only way to lose weight is to run a calorie deficit; burn more than you take in. You can do this by exercising (burn more) or changing your eating habits (take in less). Both would be best. Diets are made to be broken- you want to permanently change your eating habits in a way you can live with. What not to eat? Bad fats and carbs are two big culprits. I've completely gotten away from fast food for those reasons. Concentrate on lean proteins, complex carbs, and lots and lots of fruit and veggies. Drink a lot of water, all day. I'm not an expert; I'm sure more knowledgeable folks will join in. It would probably help if we knew what you were eating, and what kind of regular exercise you are getting.
In the last 6 months, I lost 20 lbs, and 6" off of my waist, working out 3 hours a week. I'd have probably lost a lot more, but I've added some muscle bulk along the way. Unless someone is very obese, a good target is loosing a pound a week, which is 3500 calories that you either have to cut out or burn up.