You might begin by slowly kissing your partner's breasts, lower belly, thighs and move slowly to her pubic hair. Learn the areas, places and rhythms that give her most pleasure and excitement. Start with the labia and the vaginal entrance. Move your tongue over her genital area, licking the entire vulva. Nuzzle, lick and suck her clitoris, though you don't have to concentrate there. Gently - and tenderly - lick and suck the labia.
Many women like to be penetrated by a tongue, but do it gently at first, thrusting slowly in and out. Think about changing angles from time to time, and place a pillow under her hips so that her whole vulva is more accessible. You can also use your hands to feel her breasts and her body at the same time.
You can continue in this way until your partner has an orgasm. The time taken to orgasm varies from woman to woman and with time you will recognize your partner's signals.
If you begin to get tired try changing what you are doing. Instead of licking, you can suck gently or rest by continuing stimulation with your fingers. No woman will expect you to get it right first time around. But by being aware of her needs as you perform oral sex you will help her reach climax.
Beware of your teeth! Use your lips to protect the most sensitive areas of her body, so that you don't bite or graze her vulva. Don't be afraid to ask "How do you like this?" By being alert to her moans and body movements you will probably get all the clues you need.
If you are performing cunnilingus:
Do not use your teeth at all. Cunnilingus needs only your tongue and lips in this sensitive area. Do not blow into the vagina. This can be dangerous. Vary the way you suck and lick the clitoris; be responsive to your partner's needs.
If you are receiving cunnilingus consider this:
Let your partner breathe. Keep your thighs wide enough apart to allow them some air. Let your partner rest, because cunnilingus can be exhausting to the tongue muscles. Let your partner know when you are reaching orgasm: it's important to get the feedback. Don't be shy about telling your partner what you want to do. Most people appreciate the advice.