Honestly, the best thing you can do is to make your own dog food. If you do want to stick with store bought dog food (I sure don't have time to cook healthy meals for mine
), you want to avoid grain fillers and any unspecified meats (e.g. Things labeled meat, meat meal, poultry, animal fats or any variations of these).
I personally use V-Dog and though I know many people will not agree with a vegetarian diet for their dogs, mine are super healthy on it and LOVE the taste. It is healthier for the dog than a lot of the meat dog foods sold. If given the choice between feeding my dogs grain-free, soy-free, organic vegetarian food that still provides all of their fat and protein needs or feeding my dog food that has unspecified meats that may be euthanized dogs and cats, I'm going to say that the vegetarian option is healthier