Play Biting In Puppies

Play biting is a completely normal puppy behavior. Every time I work with a client or class for puppy obedience, I am almost immediately inundated with "How do we stop the biting?!"
First off, it is important to understand why they do it. Now, I'm not always one to focus on the "why" as much as the end goal and training it in, but in this case it does help.
Puppies are not born with an understanding of bite inhibition. That is something that is taught very early on, beginning with their mother and litter mates. That's why puppy play always appears so rough. You'll hear a lot of yelping and snarls. It is a hotbed of learning canine body language, vocalizations, and bit inhibition.
Now, you've brought home your new pup and after a couple of days they are feeling more comfortable with the family and soon the rough play biting begins. And we all know those little suckers have teeth like little razors! So... what do you do?
The first instinct is to just make it stop and teach them to never bite or put their mouth to human body parts. This is understandable, but a mistake in the long run.
If we teach a pup to NEVER bite, that's a pup that will potentially never learn to control the strength of their bite... which can be disastrous later in life. A great example is a dog that has been injured. I can say from personal experience, that I am so thankful that I taught my dogs inhibition early on. A couple of years ago, my older dog, Thomas, was seriously injured while staying at my parents' home for the afternoon. I raced to their house to get him to the vet. My first instinct after seeing how bloody and hurt he was was to pick him up and whisk him to the car. Dumb! As soon as I tried to hoist him, he yowled in agony and swung his head around as if to bite at me... thankfully he only gave a warning. I attribute this to his having been taught what is appropriate and what isn't.
With pups, and even young dogs that may have just never had much work done with them, I recommend lots of play! When the pup bites, IF it is uncomfortable, let out a loud "OUCH!" This will startle them. Quickly offer an acceptable object to bite at (plushy, Kong, Nylabone, etc.) and praise when they go after that. If the play biting is gentle, I typically stop playing/moving until they let go, and then play resumes while they are gentle and biting the toys. NEVER smack or hit the pup for biting! Again, it may be instinctual, but it can lead to a dog being head shy, becoming aggressive and trying to bite again, etc. For many ears, the thing that was recommended was to clamp the pup's muzzle shut while saying "No bite!" into their face. Two problems: 1) Dog can't breathe well with the muzzle clamped shut so they begin to panic 2) Most will snap at you again as soon as you release because this action makes absolutely NO sense to them. So you've just set them up to fail and to get punished again.
If you adhere to the technique involving play and simply yelling "ouch!"/redirecting the bite to an acceptable object, you will get results. Over time, the biting will become mouthing and then will wean off. No sweat! I have had the few pups that required a "time out", (a blog on how do give a dog a time out and how long it should last to come!). When correctly, it can really drive the idea home for the more obstinate pup/juvenile.
I hope that this helps get you started! But to recap:
1) Lots of play!!
2) When biting hurts, yell "OUCH!" to break their concentration
3) Redirect the biting to an acceptable object (Kong, plushy, Nylabone, etc.)
4) PRAISE PRAISE PRAISE the biting of the acceptable stuff!
5) Remember, it's just as important to know what you want them to do in place of the bad behavior as it is to stop the behavior itself! Provide TONS of things to preoccupy their natural need to bite/chew!