By parting the vaginal lips and leaning forward to your partner's chest, you can bring your clitoris directly into contact with the base of the man's penis, and rubbing the exposed shaft of his penis against your clitoris may be all the direct stimulation of the clitoris you need to reach orgasm.
Another option is to have your lover place his thumb on your clitoris and hold it firmly in place while you move up and down, but the position of his hand may feel somewhat awkward for you both. It seems that when men stimulate their partners, they don't do it very well. Maybe he feels awkward, embarrassed or resentful. I believe most simply do not share the same sense of rhythm as their women. And it is also objectionable because you've turned your response back over to him.
For some women, changing from the missionary to the female-superior may be all that is necessary to achieve orgasm easier than you ever thought possible. Learning how to "ride" your man will make you a champion at lovemaking.
Reprinted with permission from 5 Minutes to Orgasm Every Time You Make Love. Copyright © 2000 by D. Claire Hutchins (JPS Publishing, Grand Prairie, TX).