On dogfoodanalysis.com the top rated foods (6 star) have breakdowns in the range of
Crude Protein, min. 34 to 42.0%
Crude Fat, min. 16 to 22.0%
Crude Fiber, max. 2 to 6.5%
Of course the ingredients that make up the nutrients are very important. The protein should come from meat and not beans. The fat should be animal fat and not vegetable fat. The fiber should be nutrient-dense veggies, berries or grains and not some pulp by-product (ie. sugar beet pulp).