I think these rules are about the best thing I have seen on how to eat: Simple Rules for Healthy Eating – NYTimes.com.
To make it even simpler, I would boil them down to:
1) Eat less processed food, and more food you make yourself from raw ingredients
2) Eat a variety of ingredients in moderation
3) If you have to drink something, drink water
I recommend you read the NYTimes piece, though. Really good.