1. Only animal-based proteins and high-quality refinded meals - so no vegetable-based protein
2. Don't look only at the price. The cheapest food is most of the time not the right thing for your dog. There is no need to buy a very expensive one too. You have to look what is inside the food and then make your choice.
3. Look at the age of your dog. Most of the time there are different products for different ages. (Usually 1-12 months, 1-7 years and 7 years and older)