Here's a few ideas i have heard work:
*try carrying a water bottle around with you and when your puppy does something that is not appealing to you,like the biting, spray him (not in the face).

*get an empty pop can, put in a few rocks, tape the opening and keep it hidden. then when your puppy starts this biting, shake the can but DON'T let your puppy see the can. And shout NO! they are usually scared of the sound.

*You can wrap a towel up in a roll, tie it around the middle. when he/she starts the biting, throw the towel at him/her and shout NO!!

It's best to train them when they're young because their bite is stronger when they are older.
My husband is a UPS driver and the small dogs are the ones that always nip him.
hope these ideas will work for you.
the fingers (or the fist) that the last replier suggested does work too.
God luck!