haha, have you ever ridden a horse? just bounce up and down with his penis inside you, its an amazing sensation, dont be afraid, the awesome thing about this you can control it! try moving your hips in a circle, backward and forwards and up and down. you'll find something that feels good, i guarantee it. go fast or slow depending on what feels good for YOU. you'll come by it naturally, though your legs might be a little sore for a couple of days. If you get tired, just roll over and finish up missionary style. good luck!

Well, you have greater control on speed, depth and most everything else. Straddle him and guide it in. From there, it should come naturally.