Oral sex on woman is called cunnilingus. search the word cunnilingus in google, you will find many websites suggesting different method. You can use your tongue to vibrate her vagina. visit the following webpage.
http://en.wikipedia.org/wiki/Cunnilingus. It has suggested humming into vagina. She might suggest what she wants.
Well, at the very least, don't expect to whip out your equipment and penetrate her without anything to get her in the mood. No female would like that.
Why aren't you using any protection. though?