Help!

This isn't a story. Its a cry for help.

Me and my girlfriend have been talking about masterbation for a while now, and we both admitted to doing it.

This sunday I am going to her house, and yesterday, she asked me if I wanted to lick her out. I was shocked, but I said yes, as I have dreamed about this for ages. There is one small problem with this though.

I don't know how to make a girl cum. I know it sounds stupid, but I've never known how to do it.

I want to do it really well, so she really enjoys it, but I don't know how to.

If someone could post a reply and tell me the best way to do it, i would be very grateful.