For instance, the length of the ingredient list doesn't always indicate the quality of the food. A protein from a specified animal should be the first ingredient. Avoid generic proteins such as "meat" or "poultry." Although dogs like to eat some of the animal parts we don't, proteins from a specified animal are better than byproducts. Likewise, byproducts are better than rendered meals.
Always buy the best food you can afford. When a manufacturer uses cheap ingredients, it has to bulk up the food with fillers to meet the government's minimum nutritional requirements. As a result, the portion size for cheap food is typically larger than for more-expensive food with higher-quality, more-digestible ingredients.
In the end, you'll be buying more of the cheaper food, which usually works out to be more expensive than buying the higher-quality food in the first place. Just as with humans, obesity is a growing problem for dogs. Limit table scraps; they're fattening, and some human food, such as chocolate, grapes, onions, garlic, bones and Xylitol, is dangerous for dogs.