I would just say "OUCH" Real loud when he does this...It is normal for a puppy to be nippy, jumpy, and mouthy...just let him know that it hurts you by saying ouch. Also I when I encounter a puppy that is constantly going after hands and stuff I try not to pull my hands away so much...in my opinion the puppy might think you are playing with him...so I will keep my hands and whatever very still and say ouch until he calms down.
Also keep his mouth busy by giving him bones to chew on...you can either let the puppy chew the bone by or away from you on it's own...or if you still want the puppy very close to you...you can hold on to the bone for the puppy...
Since this time is so important when it comes to teaching manners and mouthy behavior is a natural puppy thing it is important to encourage good behavior all the time. Also stay calm and never physically harm the puppy..
make sure the puppy is getting enough exercise and always have treats on you so that you can reward the puppy when its calm or did something good.
Another good thing to teach a puppy is "settle". when the puppy is jumpy and mouthy, you can roll the puppy onto it's side gently holding his head and butt down. once he settles down you can start saying "good settle" and as long as he is completely still you can start petting him. then for him to get up you can say "Break" and give him a treat if the behavior is still calm.
but remember to try to resist yourself from pulling your hands away from the pup b.c then it turns into like a game and might make them want to try to get your hands more. Just say "Ouch" and provide bones, kongs, give treats when calm, and try to raise him to be as calm as you can
