Puppies chew. They chew on wood, clothes, hands--anything they can get in their mouths.
Chewing is an essential part of their emotional and physical development, as they learn how they can relate to the world around them and as they deal with the discomfort of teething.
They learn how hard they can bite another dog through their interactions with their mothers and their littermates. When a puppy bites too hard, the other puppy runs away. If the puppy continues to bite too hard, none of the other puppies will want to play with him. He quickly learns that he needs to bite soft if he wants to continue to have fun.
Then a puppy encounters humans, who want to play but don't allow any biting. A lot of times, when a puppy bites a human, the human yells and scolds. The puppy may not recognize the continued attention they get as a correction, and they may continue to bite harder and more frequently than their owner would like.
One appropriate way to correct biting behavior is to react like another puppy would. Yelp or make some sort of sharp, fast sound that lets your dog know that the bite hurt. Immediately withdraw from all activity with the puppy. Get up and walk away, leaving the room if necessary. Or simply bring your hands to your sides and completely ignore the puppy.
When the puppy calms down, re-engage him in play. If he bites again, act the same way. He will learn that when he plays with people, he needs to keep his teeth to himself.
Make sure that your entire family is involved in training bite inhibition. All family members should give a short, sharp sound if the puppy uses teeth and immediately end the interaction. That way, the puppy will learn that he should keep his teeth to himself in all interactions with humans.
Sometimes, this behavior modification technique doesn't work. Especially in the case of an only puppy, or a singleton, the yelping sound gets the puppy more excited and withholding attention just makes him engage in escalating behaviors to get attention.
A more direct training method would work here. Get a clicker and teach the puppy that the clicker means reward. Click it and give the puppy a treat immediately. If treats don't motivate your puppy, pet him right after you click. Repeat this until the puppy associates the click with the reward.
Then, keep the clicker handy while you play with the puppy. If the puppy mouths you, say "uh-uh" and wait for the puppy to release. As soon as the puppy releases, click and then give the reward. Continue this method until the puppy learns that he gets rewarded when his teeth are not on people. If you see the puppy start to bite then pull back, click and reward.
This method is very effective, and it will help you with further obedience training. But, it can be hard to manage a clicker, a treat, and a playful puppy all at once. Try a Click-and-Lick clicker or a finger clicker to make it easier. Or use a word to mark the correct behavior and then provide the reward. The word should be one syllable any family member can say fast enough to mark the behavior--"yes" works really well, "good puppy" takes too long.
The best part about these training methods? The entire family gets to play with the puppy and engage in learning in a fun environment. This increases the puppy-owner bonds and teaches the puppy that training time is fun time.