Socialize and obedience training!
Take your pup anywhere you safely can. Expose him to all kinds of people, from elderly to babies and crazy, hyper small children. Expose him to other animals if you can, such as cats or chickens. When my puppy was too young to go for a walk I would actually put her in my double stroller next to the baby while my 3 year old rode her bike. So at 9 weeks she was seeing geese (we live by a lake), people on bikes, cars, blowing leaves (she thought those were fascinating), other dogs, garbage trucks, delivery trucks - all great stuff! Expose him to different surfaces such as tile, wood, stairs, etc. The more you can get him used to before 16 weeks, the better. You can also start doing some basic training for 1-2 minutes at a time. Use a few bites of his food or some training treats and practice sit, down, and come. I would walk around the living room or my house and say "C'mon Ripley!" And when she followed, I would praise and treat. So she learned very early on that "C'mon" means, follow me. It's easy stuff that young pups can do! Also, start crate training.