It depends on the dog, really. Some dogs do really well off all grains, some need grains. Some dogs do really well on a high protein diet, others need a lower protein diet. It's a lot of trial and error.
Personally, I stick with foods with named meats- duck or chicken as opposed to poultry. I prefer meats to be most of the first 5 ingredients. I would avoid corn and wheat even if I were feeding grains. (I don't, my dog gets ear infections if he eats grains.) I also won't buy a food with sugar, food colouring, BHT or menadione in it.
Other than that, make sure to rotate proteins regularly. The reason chicken is such a common allergy in dogs is that almost all grocery store foods are chicken based. Anything you get exposed to day in and day out for years can lead to an allergy, so it's best to rotate. I do a bag of lamb, then fish, then pork, then duck, repeat.