By now you're probably quite exhausted by your puppy-raising efforts. Hopefully, though, you are justifiably proud of your well-mannered, well-behaved, highly socialized dog with dependable bite inhibition. The challenge now is to maintain your dog's stellar qualities.
To ensure that your well-rounded and well-schooled puppy remains a mannerly, well-socialized, and friendly dog throughout adulthood, your dog needs to meet unfamiliar people and unfamiliar dogs on a regular basis. In other words, your dog needs to be walked at least once a day. Your puppy may be taken for rides in the car and to visit friends' houses as early as you like. From the time your puppy is four months old, walk him on a regular basis — at least once a day.
The prime purpose of puppy husbandry is to produce a friendly, confident, and biddable pup, so that you can face the behavior and training challenges of your dog's adolescence, and your dog can deal with the immense social upheaval that dogs, especially males, face as they navigate adolescence. It is much easier to approach doggy adolescence with an already socialized and well-trained dog. However, maintaining your dog's socialization and training through his adolescence can be tricky if you don't know what to expect and how to deal with it.
Behavior is always changing, sometimes for the better, sometimes for the worse. Things will continue to improve if you continue working with your adolescent dog, but they will definitely get worse if you don't. Both behavior and temperament will tend to stabilize, for better or worse, as your dog matures around his second birthday for small dogs or third birthday for large dogs. But until then, if you don't keep on top of things, there can be precipitous and catastrophic changes in your dog's temperament and manners. Even when your dog reaches maturity, you should always be on the alert for the emergence of unwanted behaviors or traits, which you must quickly nip in the bud before they become hard-to-break habits.
Adapted from AFTER You Get Your Puppy by Dr. Ian Dunbar