start with circles. Slow wide circles, which get smaller and smaller over time. After you ran some smaller circles around her clit, go for a couple of vertical slow licks, your last ones sucks hold on her clit and you pull it out. If you're really confident, use your tongue while you're sucking, although I only manage to pull it off less than half of the time.
After you let the clit go, press the pubic lips back, fully exposing the clitoris, and tap against it with your tongue. Now move your tongue from left to right, only hitting the clit every now and then. Go around it most of the times.
By now she should be good and wet, get some fingers in there and make the "come here" movement with your fingers. This is a 99% guarantee that you're hitting the g-spot (it feel like a sponge) and your girl will go crazy.
Now, a tip for your enjoyment; once she good and wet; you'll notice girating hips, uncontrollable moaning, etc... walk away. Just stop, give her a final kiss on her clit and get up and walk away. Tell her to come with you. Walk to whereever you feel like having sex. The couch, the kitchen, the laundryroom, the basement, the neighbors.... it does not matter. She's hungry for the D and she'll do anything to get it.