Puppy nipping

My pit bull is about 3 months, And he has those incredibly sharp puppy teeth. He nips when he's excited. As soon as I get home he is happy to see me and his tail wags but he starts to nip and chew on my fingers. How can I teach him not to do this?? I've heard of people shoving their thumb in their mouth and putting pressure on the bottom jaw under the tongue. Not sure how I feel about this