I look for meat as the main ingredients in the food, preferably a few different meat sources. I like to see eggs included and organs (not to be confused with by-products, though I know those have their place in an animal's diet, just not in a highly rendered and processed one, IMO). Basically I want to see as few glutens in there as possible since these are very hard on a cat's kidneys, especially with kidney failure being the #1 killer of cats these days. You want something with a low ash and magnesium content so it's easy on the bladder and urethra. Aside from that, you just want it to be as close to what they'd eat in the wild as possible, which is meat, eggs, bone, organs, and no grains or veggies.