There are many things you can do to increase the likelihood of the female orgasm with a partner. First off, some important information. The average woman requires about 12 to 15 minutes of direct clitoral stimulation to be able to reach orgasm. That is about 2 to 3 times longer than most men are able to last. Add to that the fact the clitoris is not located right by the vaginal opening, in most cases about 2.5 cm above the opening and you start to understand why intercourse may not be the most efficient way for women to orgasm.
Only about 30% of women are in fact able to orgasm by intercourse alone. This number can increase substantially by using the Coital Alignment Technique (CAT) that emphasizes pelvic rubbing of the partner to the clitoris. Most women orgasm easier by oral sex and direct manipulation of the clitoris and the vagina. As in the classic Kama Sutra technique of using both finger(s) (for the vagina opening) and lips (suction) for the clitoris at the same time.
Other things worth mentioning are; make sure her feet are warm. Women register cold as pain and this makes it harder to reach orgasm, this is really true! Many women have a hard time staying focused on the body sensation and find that their mind wonders. A good way to combat that is to imagine an erotic scene in your mind. Then play little details over and over again in your mind until your body takes over. Finally take time to fully relax and get into the mood before you get started. A relaxed state is a necessary precursor for an orgasm to happen.