I have always eaten right and made my food from scratch. But occasionally I would eat something that later I would regret. I read "eat to live" by dr. joel fuhrman and decided to be more careful about the food.
I never buy any precooked and prepped foods because they contain added sugars, colorants, stabilizers, etc. I cook using fresh veggies that I actually peel, slice or chop and cook myself, sometimes I use frozen ones but I read labels to check if they don't contain anything else. I hardly buy any junk food or eat out. My only rule about food is that if it could grow on a farm or be raised on a farm I may eat it.