It is very normal to feel nervous about French kissing for the first time. I'm sure she will understand if you're nervous or haven't done this yet. But it takes practise in order for someone to be able to do it without thinking about what to do. After the two of you have kissed a few times, ask her what she likes about it or if there is something you can do that she enjoys that you haven't done before. Definitely close it once in a while while kissing.
Variation is very exciting in a kiss.
Kissing only one way can be a bit boring and tiresome if the kiss is lasting a long time. My boyfriend and I have been going out for about a month and the relationship is great except our French kissing. We both seem to have two completely different styles in kissing and can't seem to get our tongues in sync no matter what. I would suggest talking to him about it. You tell him how you like to use your tongue and have him tell you how he likes it.