FINGER NIPPING GOOD!!
   I must confess even my puppies have nipped at a finger now and then or tugged on a pant leg.  I have tried to explain that humans have no sense of fun in this regard but it takes them a while to understand.

   If your puppy nips at you he is just wanting to have a bit of fun doggie style.  Do exactly what I do when a dog nips me too hard, yell.  At first a little yell could be sufficient.  However, if he just thinks you are enjoying the game then scream...use your drama.  Then be still and stop the game.
  That is what we dogs do to tell another that they are playing too rough.  Let's face it with you humans nipping is always too rough so you have to let your puppy know right away that it is just not your cup of tea.  Perhaps find a tug tug toy or some other thing you can do together that is mutually enjoyable.