The biggest area for new refs is confidence (see the theme in the thread?). Doesn't matter if you are not sure about a decision, you have to sell it with confidence. Especially with the whistle. Blow it hard, it's not just for you and players around you. It's for everybody to hear, even the spectators.
Second is effort. Put the effort in (being here give me a hint that you intend to). Be close to play but not too close (10-15 yard is good) otherwise you will get in their way. That's the only thing about positioning you should think of for your first game. Will get more advanced with experience.
Another common thing with new 'enthusiastic' refs is making it complicated. Don't over think it. Simplest answer is often the correct answer.
Enjoy