I used the following guidelines in selecting a puppy food, based on info from The Whole Dog Journal:

Quality Foods Should Contain:
-Superior sources of protein, either whole fresh meats or single source meat meal (ex. chicken meal rather than poultry meal)
-A whole-meat source as one of the first two ingredients.
-Whole, unprocessed grains, vegetables, and other foods. Nutrients and enzymes are more likely to be found in unprocessed foods.

Quality foods should contain a MINIMAL AMOUNT of the following:
-Food fragments - lower-cost by-products of another food manufacturing process, such as brewer's rice and wheat bran...Manufacturers usually include at least one fragment to help lower costs. Beware any food that includes several fragments.
-Meat by-products (not handled as carefully as whole meat) - any food that contains meat by-products as the MAJOR protein source indicates a low-quality product.

HIGH-QUALITY FOODS SHOULD NOT CONTAIN:
-Fats or proteins named generically (ex. animal fat/poultry fat instead of beef fat/ lamb meal)
-Artificial preservatives (BHA, BHT, ethoxyquin)
-Artificial colors.
-Sweeteners (corn syrup, sucrose, ammoniated glycyrrhizin) to improve unappealing food
Propylene glycol - a toxic substance when consumed in large amounts; added to some "chewy" foods to keep them moist.