I basically go through a 3 step process when I prepare for food shopping:
1) Search for whatever fresh food (fruits and vegetables) are on sale for the week.
2) Check and look for USDA Certified Organic foods.
3) If on sale and non-perishables, buy in bulk. I've read that most food manufacturers offer their coupons/sales on a 12 week cycle, so I try to buy enough based on my consumption for a 12 week period.
I also try to limit fast food to only twice a week. I know a lot of friends that view fast food as a treat from "not cooking at home," but it is actually pretty easy to bake food or cook via a crockpot.