lick the head of his **** and down the shaft and back up. Try working your mouth down on it till you can get it in your mouth some.
Use your toungue and hands...and be sure to tell him how big he is. PS if you're comfortable with the guy, enough to swallow a little pride, a little gagging isn't usually a turn-off. But don't do that if you aren't down.
A right hook will easily give him a broken jaw, has nothing to do with my mouth size ;)
use your hands
what iwantitnow and luckypickle suggested ...
You can use your hands as well.