When performing the following, make sure that your fingers are well lubricated. There is nothing more uncomfortable (and painful) than a dry finger roughly rubbed across a woman's clitoris or pushed inside. See the sexual lubricants product page for information on useful lubricants. In most cases, proper foreplay stimulating a woman’s erogenous zones will usually avoid the problem of dryness. Nevertheless, it never hurts to keep a "tube of lube" sitting nearby. Under no circumstance should you put pressure or blame on your partner for this if it happens; work with her to get around it. It’s written all over this and every other sexual information site, but in case you have forgotten, communication is key.
Most women masturbate by rubbing a finger or two over their clitoris, sometimes "through" the skin of their inner or outer lips, in a circular or back-and-forth motion. You can do this too, and it is most helpful to ask, or better yet, have her show you how she likes it done. Lie down side by side, and put your hand over hers while she shows you what she likes. You can also try having her hand over top of yours guiding.
Another technique which women are very receptive of is to have your partner lie on her back, spread her vaginal lips wide apart with your outer fingers, and use your middle finger to rapidly slide up and down her vagina rapidly and lightly grazing her clitoris. This motion alone will often bring a woman to orgasm. Don’t forget to use your mouth while you are fingering, keep kissing her, her neck, and all her other erogenous zones.
An excellent way to begin manual stimulation is to stick one, and later two or more, finger(s) inside her, with your palm cupped over the mons area. We're talking about that fleshy "mound" over her pubic bone. Your finger should have freedom to move in and out freely while the palm of your hand can add pressure against her vulva and clitoris. Once you get better, you can start moving your palm to add more stimulation.
Another, more intense motion is to position your hand so that you have one or two fingers inside her with your palm facing her body. Now bend your fingers inward and move them in rapid but short movements focusing on her G Spot. This technique can quickly bring your woman to orgasme.