I've been around the same weight my whole life, with slight fluctuations due to laziness/business. For me, simple things like drinking green tea (which is a metabolism booster, unless I'm wrong), eating whole grains, and avoiding too much fast food usually work well (common sense, I know). Aside from that, little things like going on the bike while you're studying and spending an hour every two days going to the gym or playing a sport work out great. Light weightlifting even helps, regardless of whether you want to put on muscle or lose weight.