First of all, you need to decide between weht and dry food. Dry food is often better, because it helps maintain tooth health and can sit out longer without becoming too gross. However, puppies have sensitive stomachs, and some just can’t digest dry food yet. Some trial and error may be in order here.
Whatever you get, name brands aren’t always important. Rather, it’s the ingredients that matter. Make sure that the first ingredient is an animal protein that is named, like chicken or lamb. Some people prefer not to feed their dogs food that contains animal meal or by-products, but these are generally safe and acceptable — “meal” just means that it’s more concentrated and “by-product” just means that it’s an animal part that isn’t usually consumed by humans (a chicken stomach or esophagus might not sound very appetising to you, but I promise your dog won’t mind, lol). However, it’s best to avoid foods that contains food dyes or Butylated Hydroxyanisole (BHA), Butylated Hydroxytoluene (BHT), and Ethoxyquin. Food dyes are difficult to digest for dogs at any life stage, BHA and BHT are known carcinogens, and Ethoxyquin is toxic. Make sure your food was made in the USA (or your local country) as foods made in foreign countries might not have food preparation guidelines quite as strict as the local ones. Also, for puppies, it’s probably best to feed them a food that’s grain free, as grains are often difficult for dogs to digest. Vegetables are not only acceptable in dog food, they’re good for the dog (unlike cats, dogs aren’t true carnivores, and can often eat some veggies).
It probably goes without saying, but make sure whatever you get is formulated for puppies instead of general dog food, as puppies have different nutritional needs than adults. Also, if you have an unusually small or large breed, you may want to look for foods specific to those sizes, as smaller puppies may find it harder to eat large pieces of kibble and larger breeds need extra calcium to grow those larger bones.
People are suggesting homemade foods. Don’t get me wrong, those are great. However, they require a lot of extra work on your part: researching a “recipe”, purchasing the ingredients, making it, having enough containers and space in the fridge to store the end product, etc. It’s also easy for things to go wrong, such as not meeting all the vitamin and mineral needs or going to the store and finding that they’re sold out of a key ingredient. For the average person this isn’t really feasible. We fed our dog homemade food for a few months, as she was an adult dog but has a very sensitive stomach and could digest homemade easier than store brought, before giving up after the second time the store stopped carrying an ingredient and just getting higher quality store brought.