You should start imprinting/training your new puppy the day you bring him home. I do not mean that you should embark on teaching him “commands” just yet, but you can make a positive impact on his future behavior by the way you handle him and introduce him to different situations. Remember, his character will be in large part formed by the time he is 4 months of age. You don’t have time to just passively observe his puppy cuteness. You need to become informed by way of studying the latest in puppy training and be proactive. If you don’t, then someday very soon you will look up and see an adult sized version which may not appear to be cute in the least as he is using your house for a bathroom or eating the siding off of the house!
The first things that I would recommend that you tackle would be getting him accustomed to being handled, crate training, and housebreaking. As always, feel free to leave your questions or comments!