I follow these simple rules:
1. Cook your own food from fresh ingredients.
2. Do not use canned food. There are additives in the can linings that are questionable at best.
3. Read all labels. Even foods such as sausages have labels. This is important if you have any problems such as gluten intolerance as some sausages are made with bread crumbs.
4. Avoid things like "natural flavourings". This means the additive is obtained from a natural source; but, it might not be something you want in your body. For ex: one source of natural flavouring is from a special gland found in beavers.
5. Eat whole foods such as whole grains, unrefined flour, etc.
6. Make the majority of your diet vegetables and fruit.
Hope this gives you food for thought.