My advice would be not to put too much pressure on yourself. Beint that it's your first time, you may be going into it with a lot of romantic ideas of what it should be like and so forth.
One thing is certain. You will never forget your first time. Even so, don't put so much pressure on yourself to make it perfect. Your first time doesn't have to be, and usually isn't, the best time of your life. If it turns out to be incredible, that's all the better. If it doesn't, it's no big deal. Just look at it as a stepping stone to future sex sessions. Some will be great, and some won't.
As I look back on my life, the times I enjoyed the most were times when I was relaxed and just let things happen as they came.
She is experienced. I'd let her take the lead a little bit and just enjoy the ride.
Good luck! (Why am I saying that? You already know you're going to get lucky. LOL) :1orglaugh