Avoid all foods with hydrogenated oils (promotes heart disease.)
Avoid homogenized milk (promotes blood vessel plaque, heart disease.)
Eliminate excess sugar and high fructose corn syrup. Substitute with agave nectar which is just as yummy and very low glycemic. (promotes diabetes and creates inconsistent blood glucose levels which promote obesity.)
Avoid refined carbohydrates, substituting whole grains, vegetables, sweet potatoes, nuts, legumes, berries, greens, etc. Substitute wheat for quinoa and teff. Substitute white rice for brown rice. (Refined carbs deplete B vitamins and promote glucose instability.)
Avoid all meat packed with sodium nitrate (promotes colon cancer). Look for "uncured" meats.
Avoid artificial sugars, flavors, colors. (Nearly all of them have unfortunate side effects.)
Try to get 90% of your protein from plant sources. (excess animal protein is associated with disease)
Go outside! (Sunshine promotes vitamin D which is critical for immune function, and vitamin D strongly prevents cancer.) While you're there, exercise! :)
Read: The China Study by Dr. T. Colin Campbell, Cancer-Gate by Dr. Samuel Epstein