You cannot keep your puppy in a "sterile bubble" and his socialization needs during this time are extremely important also. It is a balancing act. The best advice is to avoid taking him places that dogs of unknown origin frequent, such as rest stops on freeways or dog parks. Other new puppies are high risk also. Your pup needs to meet a variety of people and other dogs, be taken places in the car etc. It is fine for him to play with your friends or relatives dogs who have been well immunized and are healthy. Most vets will agree that your pup can go to Puppy classes after the age of 16 weeks. Puppy classes, and later regular obedience classes, are highly recommended. A well-trained dog has a good ego, and feels secure and loved.