Relevant developmental periods in canine:
1. First Fear Imprint Period
2. Optimum Bonding Period
3. General Socialization Period
1. First Fear Imprint Period: 6-10 weeks
During this first period puppies are extremely sensitive to positive and negative experiences and extremely impressional. It is very important to avoid any training that involves negative and abrasive techniques at any age, but especially during this period. This is why positive reinforcement training is so important. Positive reinforcement rewards the puppy for something good s/he has done, and therefore the puppy will want to engage in this behavior again and again throughout its life. When someone refers to "this thing that happened that scared my dog for life," they are probably referring to a negative incident that occurred during this period.
2. Optimum Bonding Period: Begins at 7 weeks
This is the time a puppy is most likely to bond with other dogs and/or people. This is why 7-8 weeks is the age most often recommended for people to bring home their new puppy. Bonding with your pet is very important for many reasons. You want a strong positive bond with your puppy so they will continue to be the dog you have always wanted throughout their life. A dog that has a strong bond with his/her owner will listen to commands and respond better and be more overall focused on their owner.
3. General Socialization Period: 7-16 weeks
Once your dog has been properly vetted and given the okay to interact with other dogs, it is vitally important that you socialize your puppy AS MUCH AS POSSIBLE! An under-socialized dog is much more likely to be frightened, misbehave, and possible bite someone in the future. The more you can socialize your puppy to every situation possible, the more comfortable your dog will become with anything you can throw at them in the future. For example, when my oldest dog, Nekita, was a puppy, I took her everywhere I possibly could with me. To the park to go swimming and grill out with friends, to another person's house, to a party, and for walks in busy areas with lots of commotion. Anywhere and everywhere I possible could take her, I did. This is why today, I can take Nekita anywhere, even leave her overnight with a friend, and she is fine. She does not get anxious or nervous, she does not wine or pace, and she does not get scared when finding herself in a new situation or place. The best thing you could ever do for your puppy is to proper socialize him/her!