I have a saying about me eating pussy. I say "When I eat pussy, I go from bellybutton to asshole, kneecap to kneecap".
I would recommend that you go slow, you lick you gently suck, when she moans louder you do more of what your doing. You look up at her ask "what else do you want me to do?" Have fun with it, laugh when you do something, giggle. Gently bite, if she tries to push away do something different, if she grabs the back of your head and tries to push it up her pussy, your doing her good. Ain't nothing like a girl grinding her crotch all over your face, yelling "oh GGGGGOOOODDD!!"

Rinse and repeat. Most girls will stop you after once cause it's so intense, but if you can get them going again, a second orgasim by mouth you will have a loyal, faithful girl that brags about your ability to all her friends.