All puppies bite, at least they mouth and play bite.  This is how they explore the world!
Inappropriate, hard biting should be curbed very early by teaching them to have a soft bite.  
They must learn this because as they grow their jaws will become stronger and they are more
likely to cause damage if they have not been taught at a young age to have a soft bite.  

Bite Inhibition:
Think of the  pressure of your puppy’s bites on a scale from 1 to 5.  5 being very hurtful and
1 being that the teeth just touch the skin.  At first you must “yelp” (very high pitched, short,
loud noise) at all the 5’s.  Your puppy should stop and look at you.  Praise him for this. When
you yelp you should not pull away.  Teach your pup that he should stop when he hears the
yelp. Also, if you pull your hand away, he may think you’re playing and grab again.  Once the
5’s are no longer occurring, yelp at the 4’s.  Again, praise your puppy for ceasing his bite.  
Once the 4’s are gone, yelp at the 3’s and so on until you yelp when your puppy puts his teeth
on you.  The yelp should include not only skin but clothing too.  Teach this to older children
as well and make sure to supervise them as they are closer to the floor and may seem like
playmates for puppies.  This is the way dogs at play teach each other that play has gotten a
little too rough.  Have you seen two dogs playing and one yelps?  The other immediately stops
and looks at the other dog.  Playing then resumes and usually both are happy because the
biting is softer.

If your pup is in a wild mood or just does not respond to the yelps, get up quickly and ignore
the dog for a minute (go in another room if you have to).  He must understand that if he bites
too hard, his playmate goes away.  Do all of this calmly.
            
Also, make sure that no one in the house plays rough “hand” games with the puppy.  He should
only play with people with his toys.  Make sure children know that when your pup starts to
get too crazy, they should stand up, cross their arms and be very still.  Jumping up and
pulling their arms away will only entice the dog to bite more.  No running around the puppy
either.  

One last method to teach your pup not to bite humans:
Tether the dog to something strong in the house. Start playing with the puppy and his toys.  
If he accidentally, or purposely bites the person instead of the toy, immediately stand up,
step out of his reach and turn around.  Ignore the pup for a minute or so.  Try to play again.  
Teach him that if he bites his person, play time goes away.   

Also use interactive toys like Kongs  keep your puppy busy and to place his biting and  
            chewing on appropriate objects.
The Truth About Puppy
Biting