1) train the puppy on leash.
2) reinforce the SIT command, making sure BOTH front paws are on the floor each time you reinforce it.
3) set the puppy up in a situation where he is going to paw. WATCH HIM CLOSELY. As SOON as one of the paws starts to come up, put strong upward tension on your lead, and demand him to SIT. As SOON as both front feet are on the floor, immediately release him with OK!!, and whirl him around to face AWAY from the visitor, and food reward him.
4) Repeat repeat repeat.
Reward both front feet on the floor.
Interrupt, correct to the sit with both front feet on the floor EACH time he starts to paw. Then whirl him away from the visitor, sit again, and reward.
Once he is pawing less, you might change your verbal command to :4 on the floor" or something like this.
The main things you need to do are:
1) CONTROL the puppy with your leash
2) TRAIN a CONFLICTING BEHAVIOR (ie, he cannot paw while sitting with both front feet on the floor)
3) INTERRUPT with your leash each time a foot comes up to paw, and demand your sit. Release from the sit with strong verbal praise as you turn him 180 degrees away from the person who is the distraction.
Practice, practice, practice.
