The worst kept secret in the world (the world of beddie things, at least) is that we have more (and better) orgasms when you perform orally than when you are "hammering away" (as Jenna so aptly put it).
Do it gently, then roughly, then gently again, but always enthusiastically.
Make a girl feel as though having her c u m m i n g into your mouth is what you want more than anything in the world (let her kneel over your mouth and that is exactly what will happen).
And buy this. If you can't find it an a shop, order it from Amazon. I don't know whereyou live, but I got a copy from a shop called Harmony near Tottenham Court Road, opposite CentrePoint.