The man should thrust and at the same move his thighs diagonally slightly rubbing her vulva and clitoris with his belly. This position is much more superior to standard missionary position because his penis stimulates her pussy in a different more unusual angle and the rubbing stimulates the clitoris. At the same time the woman is not burdened by his body weight which allows her to concentrate on the orgasm not other dominating signals of her body. This position is very good, because it allows the man easily to stimulate her clitoris while thrusting. At the same time it is very comfortable position for the woman, and she can be very relaxed.
Many women tend to enjoy it very much when both of their holes are penetrated at the same time.
Try it also out in other positions where convenient. Doggie style, but important thing here is to reach with your hand around her body and stimulate her clitoris while thrusting. Without such stimulation, many women experience difficulties reaching orgasm, because thrusting penis alone does not provide enough stimulation. Otherwise many women like doggie style very much because it is very comfortable, just be sure she can rest her knees and elbows on something soft. She will enjoy very much a position, where she sits in his lap wrapping her legs around him and both partners facing each other.