There is not a right way to do this, there is a right way for you. First, adopting from the classifieds is fine (its how I found my lab) but the key is to visit the dogs and find one that has the personality you are searching for. The number one problem is people get enamored by a cute puppy and don't follow the clues the puppies are giving you. For instance, the puppy I adopted was located in Orlando (where my parents live) I asked my Dad to check it out first since he was there and he knew the type of dog I was looking for. When he got there the puppy came right up to him and started licking him and following him, etc. So we knew the puppy had what I wanted - excellent social skills. The dog wasn't pushy or dominant, etc.
So, my advice is check out all your options - but know what character traits you are looking for right off the bat and don't deviate because you got sucked in by cuteness. If puppy is aloof and dominant, you should probably avoid unless you want to put in extra time for obedience trainings. Have a plan of what you are looking for and stick to it.