1. Stay away from sugar and don't eat alot of bread. Eat fruit, vegetables and protein (nuts, meats, etc). And when I say stay away, I mean completely remove them from the house.
2. Eat 4 small meals, rather than 3 big meals, this makes you less hungry through out the day and less likely to binge on chocolate and whatnot.
3. Limit most of you liquids to water.
4. Run. Start with a slow jog or even a walk for about 15 minutes, move it on from there. I usually run 3 miles twice a week.
5. Take up a sport, maybe play basketball at the gym with your friends once or twice a week. 2 years ago I was at about 35% BMI (fat to weight and height), since I've started wrestling I've gone down to 15% and lost about 30-40 pounds (185-155), and that still fluctuates daily, I've seen wrestlers lose five pounds of pure weight, not water weight, in two days to make it into a different weight class. It's all about determination and a having a goal in sight.