It's actually pretty simple. It all comes down to three things.
1. The vast majority of your food should be un- or minimally processed. Meaning, the closer it is to the way it was when it came out of the ground (or off the animal), the better. For example:
- Real Cheese > Kraft Singles
- Brown Rice > Rice-a-roni
- Olive Oil, Coconut Oil, Real Butter > Margarine
- Water > Kool-aid