Let's start on the right foot: Women masturbate. It's completely healthy. There seems to be more open discussions and social acceptance of male masturbation because "men think about sex all the time." But the fact is women also have sexual needs to fulfill, and masturbation is a healthy way to satisfy those needs. Sometimes there's just no time to wait for that perfect partner!
Masturbation is a good way for women to get to know their body and to find out what brings them pleasure. For those who are having a hard time reaching orgasm during sex, or those who feel uncomfortable or embarrassed with themselves during sex, it might help to masturbate. Masturbation can help you gain a higher level of comfort with your body and a higher level of relaxation when naked. This can make sex more enjoyable and an orgasm more attainable. For those women who can only reach orgasm by masturbating, and not by having intercourse, you can increase your chances for orgasm by learning what brings you pleasure during masturbation and communicating how you do this to your partner. Also, by regularly masturbating you will become familiar with the normal amount and smell of your lubrication. This will enable you to quickly detect odd conditions for which you might need to visit a physician.
In general, women tend to be like a computer with many application windows open- so many things on her mind at once. Maybe that's why some women have a hard time enjoying sex fully. (They're too busy thinking "I must look really funny in this position," "oops, I forgot to shave my legs," "what am I going to wear tomorrow?") While you masturbate, concentrate on the pure pleasure of the act and try different touches, speeds, strokes, positions, whatever you are curious about! You may find out that you need external help to put you in the mood and keep you there. You may play sexy music, light a scented candle, put on a silky gown, put on some perfume, etc. Maybe that's what it takes for you to immerse yourself in the moment. Even if you don't need any help, these things provide more to enjoy!
Wash your hands. Go ahead and touch yourself, let yourself react to the movements. Start caressing your clitoris with your fingers, slowly at first. Move your fingers sideways and up-and-down, varying the speed of your fingers. You may feel your outer lips grow as you continue to masturbate, and as they do you may start to feel lubrication. Caress your breasts with your other hand if you'd like. When you are ready, slip your finger(s) into your vagina and move it up and down. Be careful of your long nails, they could damage your vagina. Depending on your comfort level, vary the depth of your reach. You may find that reaching the roof of your vagina feels great, in which case you may want to lay on your stomach for a better positioning. Squeezing your butt helps to tighten the muscles and intensify the experience. You could also look into using other methods besides your fingers. You may purchase a dildo at a pleasure store and experiment with it. Be mindful to get the right one for you, the size, what it does, etc.
If you are comfortable, look at yourself in the mirror as you do this. See the beautiful woman lost in the passionate pleasure? That's the woman who is comfortable with her body and her sexual needs; she knows what pleases her. And that's the woman your partner will see while s/he is making love to you.