one thing I found by reading then practing and trying this once was while tickling the balls with your tongue, his cock in your mouth- while drawing back up flatten your tongue against his shaft and have it wrap around and flap it, like a soft slap as you draw off him or harden it to a tip and flicker it fast back and forth.
Deep throating used to make me almost orgasm instantly, feeling the head penetrate and stretch that tight portion at the back of my throat was indescribable so one can only imagine what it would feel like for him.
Also using your lips, tightening and softening them at the same time as if playing an instrument...and wetness, lots of slippery wetness to fluctuate and alternate pressure and movement.