Use color in your planning. Vibrant color usually equates to better for you -- beets, oranges, etc.
Read the nutritional labels on products.
Avoid too much sodium, calories from fats.
Be aware of empty calories in a lot of soft drinks and liquors.
Avoid highly processed foods -- whole grain is better than cracked wheat, etc. Avoid packaged foods.
When eating out, be aware of caloric values if possible. Avoid fried foods and heavy, cream based sauces.