My girlfriend likes this part the best;
Use two fingers and go inside slowly... (This is after foreplay but before she goes crazy) Move your fingers, in a certain rhythm/motion, very slowly inside. (For 5-10 seconds) Then slowly bring your fingers all the way out, while sliding them up across the clit. Then slowly bring them back into her vagina, while going over the clit again, and repeat. Get a good slow rhythm going. I haven't really tried going to to fast because she just loves everything done slowly. I guess the key is going slowly.
Don't forget about kissing her and telling her how beautiful she is or how much she means to you. That may not sound like much but she WILL remember it afterwards.
Does anyone have a good position to finger and eat a girl out at the same time. I usually just lie in between her legs while she's on a bed. It's just kinda hard to finger and eat her out at the same time.