What to look for?

What should I look for in a dog breeder? Like good things they should have before I consider buying a puppy? I'm looking to get a purebred, not sure what breed yet, but want to get the pup from a good breeder.

*added*

I am not going to a shelter or rescue. I already have a rescue dog and I'd like to buy from breeder this time around. Thanks though! (: