Hand moves

What shall I do with my hand? Any movements aside from in and out? My hand is past his prostate, do I pull back and massage the prostate. I only know one dude that likes this, my first time but he doesn't talk much or direct me. He likes to drive down to my mid forearm and grind, and give me this weird Popper filled grin yet doesn't make noise or talk. the last time I felt like I was a stump laying there with my arm straight up while he rode my hand and arm, felt used.