The first thing you need to do is gain confidence in what you do. With this the nervousness should subside. To be honest, you have to do what feels natural. You must communicate, learn what he wants, and he must also learn what you want. Sex is a two way street, both must give and both must receive.
I know there are going to be some guys who respond to this and will try to give you some advanced advice on how to pleasure a man and what not. Honestly, don't listen to it. This is something that takes time to develop, and while you both learn each other's bodies you will also grow closer to one another.
Don't try to rush into things prematurely. Do what feels natural, and communicate about what each other like or do not like. If you do something and his response is positive, then keep doing it.. Work with it. If his response is negative, then try something else. Likewise, you should also provide some type of "guidance" (even if it is not verbal), and he should act accordingly.
Good luck.