First off, I would suggest teasing.
Lick and kiss her inner thighs. Trace her labia with your tongue but don't touch the clit. Keep teasing until her hips are moving. Then, with a soft tongue, lick from her vag all the way up slowly to her clit in one motion. Keep your tongue soft (but pointed) until you feel her clit swell. Spread her lips with your tongue, going side to side, once again starting at her vag. With your fingers, spread her pussy lips very slow, licking softly at her clit. Keep doing this until your chin is soaked. Then, still licking, rim her hole with your finger, not going in. Tease her in this way until she begs you to put your finger in. When you do, put your palm up and press your middle finger on her g-spot which is a small lump inside. Well, not really a lump, kind of like a small...hill. Press up on her gspot, still licking her clit. Don't finger fuck her fast unless she tells you to. Most women need to concentrate on the feeling of the tongue in order to cum and if you are stimulating her pussy too much, she may lose her concentration. Don't come at it like you are starving and haven't eaten for a week. Make sure you tell her how good she smells, tastes, feels and a couple of moans showing her how much you love to eat her is a good idea too.
Oh and most important - follow any and all instructions she gives you.