The more time you spend kissing and touching her, the more stimulated your partner will become and her clitoris will be easier to locate as it will be hard and swollen. Next, move your tongue slowly around the vagina and into it, lick softly around the clitoris, slowly bringing your tongue closer and increasing pressure as you come in contact with the clitoris. If your partner shrinks back at this point you will know to apply less pressure or to just lick the sides of the clitoris. Many women are so sensitive that they cannot tolerate direct clitoral stimulation. Alternate licking and sucking or use a combination of the tongue and lips.
Many women prefer to have vaginal penetration before they orgasm rather than continued oral sex.
She will either tell you she wants you inside her or start to pull your body into position. If your partner prefers to orgasm from cunnilingus, this is the time to suck and avoid using the tip of your tongue on her clitoris as it will be very sensitive at the moment of orgasm and shortly afterward.