When adopting a new puppy, socialization is an essential part of training. The Cornell University College of Veterinary Medicine states that the crucial socialization period lasts up to about 12 weeks (3 months) of age. However it's important to continue socialization throughout their lives. Make sure to introduce your puppy to new things (people, places, other animals, etc.) in a safe and non-threatening way . By doing this, you help your dog grow into a confidant dog.

For more information, here's a great article from Dr Marty Becker at Vetstreet about how to safely and properly socialize your dog.