Include from 5 to 13 servings of a variety of fruits and vegetables daily. A serving is one piece of fruit, ½ cup of vegetables, 1 cup of salad greens, or ½ cup of juice (choose juices without added sugar or corn syrup).
Increase whole grains and limit refined grain products. When choosing grain products, be sure it says "whole grain" on the ingredients list. If it doesn't, it isn't whole grain.
Get a good mix of proteins, both animal (unless vegetarian) and plant. Eating a variety of proteins will ensure that you get all of the amino acids (building blocks of protein) you need.
Enjoy beneficial fats. Get the majority of your fats from plants and fish and minimize saturated animal fats.
Links:
[1] http://www.takingcharge.csh.umn.edu/explore-healing-practices/food-medicine/what-do-specific-foods-do
[2] http://www.takingcharge.csh.umn.edu/create-healthy-lifestyle/diet-nutrition/consider-food-medicine