Excersising more helps loads! I used to be overweight, but then I started karate, running and swimming and I've lost tons of weight. I only run now, so I've noticed the weight starting to creep back a bit, but I'm gonna do a bit more exercise and eat a little less.
The trick is not to follow those crappy fad diets, too. Believe me, I've tried ALL of them x.x Something that promises dramatic weight gain is just too good to be true! If you find yourself wandering off to the kitchen to eat, even just due to boredom, try chewing some gum instead. Sometimes I go brush my teeth if I feel like I'm gonna eat a ton of chocolate, cause afterwards I don't wanna eat anymore for a bit (the chocolate just wouldn't taste the same!)
Anyways good luck ^_^ and remember: you CAN do it! x