How Should I Kiss this Girl?

My girlfriend and I have been dating for over a week. She is 15 and I am 16. She has never kiss anybody before and I have kissed 3 other girls. I am planning on kissing her within a couple of weeks, but I don't know how to do it. All the other girls I have kissed insinuated that I kiss them. This girl I am dating isn't that kind of girl, she is really, really conservative. My question is should I ask her if I can kiss her, or should I just do it and if so how? Just so you know I really want our first kiss to be special, because it is her first kiss after all, and I really, really care about her and I want it to be special.