How do you prevent being overweight?

You can do many things:

Exercise and this doesnt just mean running as many people immediately think of and are put off by. People can do exercise through sports that they enjoy or electronic games like dance mat.

Eating healthily is a an obvious choice but it is easy to do. You can still enjoy eating calorie food but you have to make sure that you aren't eating it more than you need to.

You can eat fruit and not so calorie food that will make you full without you having to eat much. If you can get into this habit, then it will not only prevent you from being overweight, but it will also stop you from getting colds and spots (which can stress you out and make you tired).

Believe me, this is all worth it in the end. :)