Deeper isn't always better.
Warning: this gets a bit graphic
Try this simple one:
Use you tongue on her clitoris and while you are doing that curl your index finger up into her vagina. You're aiming for the 'G' spot. You will probably need to go in right up into the last knuckle. Make sure to fold all your other fingers (and thumb) back.
When she starts to orgasm, pull your index finger out to the second knuckle and gently insert your middle finger (to the same depth as your index finger) and gently and rhythmically stoke the inside wall of her vagina. Don't let off that tongue! After she orgasm slowly and lightly continue to use your tongue and remove your fingers.
Above all, don't rush. Take your time and enjoy yourself, and let her enjoy it too!
While I'm at it, let me recommend a good book: The Big O (http://www.amazon.com/exec/obidos/tg/detail/-/0767907485/qid=1080768324/sr=1-1/ref=sr_1_1/002-9632346-6018446?v=glance&s=books). You don't even have to buy it, just visit your local library. Remember, reading is fundamental!
- Who's Your Daddy?