My wife really likes a few things:
Gently suck on the clit (preferably after you've warmed her up a bit) and flick it with your tongue whilst sucking..
Inserting your tongue into the vagina I hear is nicely pleasureable too, or use your fingers or a dildo at the same time..
Once you get really good at it you can make her cum in, like, a few seconds if you wanted to. I can do this and try not to get carried away at first, so I play with the outside, thighs, etc.. to get her begging for it.
Experiment
Tell her it's your first time, ask for help and I'm sure she would be glad to help out
