Read the ingredients. You want to have some kind of meat and meat meal (from a named source...like beef, chicken, lamb, etc) as the top couple ingredients. Stay away from byproducts, unnamed meats, and corn.
My dog seems to do really well on the Purina One pro plan dog food around 40 bucks for 38lbs!....some of them have less grains..I feed him the Chicken and Rice - dogs shouldn't have too many grains in their diets. Good luck!