My 12 week lhasa apso is biting hard! Any suggestions to prevent it?

Whenever he hurts you in anyway, immediately stop playing with him and leave him alone. He wants to play with you and will learn that he can't bite you if he wants to keep playing. You can put him somewhere quiet like the laundry when he does it for some time out, but that may not be necessary. My dog learned pretty quickly just from "ow" and the play stopping. Now whenever I say 'ow' she comes over to check on me :p