1. try to eat healthy, mostly-natural foods (and you know what is healthy and what isn't)
2. don't eat too much
3. exercise every day. sweat is a good indication
it's not THAT hard folks, go look at pics from the 1910s, obesity was almost nonexistant
also:
1. there is no way to be in shape while eating crappy food all the time
2. there is no way to be in shape and never exercise at all