The most effective way I know of to do this is what you might call a reverse missionary - he lies on his back, legs spread, she goes in between his legs on top exactly as if it were normal missionary position.
This position is great for clitoral stimulation for her, but it doesn't do very much for him as there isn't much thrusting going on. What makes it so good is that he is forced to work hard but he depends on her co-operation for pleasure, and she can just enjoy riding on top and talking dirty to her slutty little bitch and asking him how he likes being fucked by a real cock.