how I can make my puppy stop biting so hard?

Very late reply, and I am sure your puppy is all grown up. However for future reference and those who wish to know.

I find with most dogs ignoring works wonders and discouraging teeth on skin contact all together. When training my Afghanhound (which is quite a bit harder because they do not look for approval from their owners as much as other dogs) every time she would go to chew on me or grab my pant leg I would her a firm but sharp 'Ssst'. An ouch or high pitched yell would work as well. However I always 'Ssst' for any and all disapproving things. Simpler that way.

Continuing on...

The first level, when the puppy starts chewing on you, yell, squeal, whatever, get up and turn away from the puppy. Ignore him/her. No eye contact, no talking, no touching. If the puppy was not to riled up to begin with they should be a bit vexed and confused as to why you did that. However if that did not work and your puppy starts jumping up, biting your pants, grabbing your hands, any other contact of your body or clothes with their teeth. Walk away. Don't make a noise, just walk away. Continuing to ignore. If your puppy follows you, still persisting. Go into a closed off room. Shut the door and stay there for a few seconds (not to long because I am sure many puppies would get stressed and pee or poop in your absence) then come back out. If your puppy continues to bite and jump, return to the closed off room. Rinse and repeat until your puppy either wanders off or has stopped nipping/biting. 

Afterwards a reward is in order. Give them a bullistick, pizzle, hoof, rubber chew or even an ice cube, (rawhides are bad for their bellies) Nothing to exciting, because you do not want them to get riled up again. Leave them in peace. Though it is probably not a good idea to leave the immediate area, or they will likely leave their relaxed state and follow you.

Good luck! 

Another good tip we had was to make a high pitched ouch when he bites as this is how his siblings would react when they bite too hard playing it seemed to help with Bailey.  You could also try standing and turning your back so he doesnt get a reaction from you Bailey never bites now these really did help us.

yes, best way to stop him from doing that is giving him something to chew on.  At this age he is slowly begining to teeth.  I had the same issue with my lab.  What i did is grab an old sock and place a plastic bottle inside it.  Not only is this a good toy, but it will cause him to bite the sock and help his gums while hid teeth begin to come out.