Start out gently, but get more aggressive based on how she reacts. Kiss her, but not the whole time. Just when it feels right. Do what feels good- that probably means it feels good for her, too. Don't be too rough with her breasts, but be sure to give them attention. Keep close most of the time. Most girls like the contact and during-sex-cuddling. If she wants to get on top, let her, but don't ask or tell her to. If you are wondering how she is liking it, ask if she wants to change positions. This just lets you make sure she is getting the right amount of pressure in the right way. It is different for every girl- some like missionary, some doggy style, etc. Finding the right position to reach her pleasurable spots is unique to her. Have fun finding out!
Oh, and if she tells you to do something, do it! :)
why don't you just ask her. that way shell tell you exactly what she wants and will always feel good. if you two are ever on the subject casually bring it up tell her you wanna know what she likes so you can please her. it might be a bit awkward but its worth it. if she doesn't know try out common moves like doggy style. or her on top.
Make sure you pay attention to her, she'll let you know what she likes and doesn't (mostly during sex, whether it be directly, such as telling you that she likes it, or indirectly, by reacting to what you do). However, do not underestimate the power of discussion outside of sex, ask her what she likes, or would want you to do, and you can then apply it.
Those are the best "skills" to have when it comes to sex.