You find a breeder who health tests for things like hip dysplasia, who is willing to disclose any health issues in their lines (and there will always be something, but it should be either way back or not directly in line, maybe a great aunt or distant cousin or something) and is familiar enough with the lines to discuss them and educate you on them. The breeder should interview you and ask you questions. They should want to know what your lifestyle is like, what experience you have, where the dog will be while you are away, how long it will be by itself during the day, etc. They will also expect you to have questions. Questions about how the pups were raised, what training they've had, what health testing the breeder has had done on the parents, any titles they've achieved, even as simple as why this breeding with these particular dogs. And they should have good, solid, ready answers for those questions.