You're on top, then through a series of moves, you turn around while he's still inside you and end up facing the opposite way. So start by riding him, "rodeo-style". Then, using your hands to steady yourself, lift one leg over your body and begin to turn sideways. Continue rotating, stopping at intervals for a few thrusts, until you're facing away from him.

He gets a unique "corkscrew" feeling on his penis while you turn around, and is simultaneously treated to a revolving-restaurant-type view of your body. His erection points out instead of up, which is an instant arousal upper. You can vary the thrusting to make things even more interesting. Grind into him slowly, then SUDDENLY speed up, or vary the depth of penetration.