This is just my 2 cents but when it comes to any actual mouth on skin contact, I think using the drop it/leave it command would send a mixed message to the pup. The leave-it command is most often used to teach a dog to ignore something and in puppy-training, it usually means they'll get a higher reward for ignoring the lesser temptation. Personally, whenever there's any mouth-to-skin contact, I go back to the basic scenario of teaching bite-inhibition and that is to let out a "Yipe!" (and I leave immediately). I'd always head to the nearest room I could close the door and I'd stay there for about 15-30 seconds, then return. Once they get that biting means you're gonna leave, they do start to catch on.
I do a similar thing with the jumping (and my 8-month old LOVES to jump up at me). If she jumps at me in "play", I give her a stern, "Nope!" and I leave te room.
It's worked for me but you'll find what works for your puppy.