As downtheroad just said, start with a short trip before you go halfway across the country.
The main advice I would offer would be to travel as light as possible. There are literally hundreds of "gadgets and gizmos" you could buy at the camping store, but most of this stuff you can live without. It is a real temptation to carry way more than you need. In our case, my wife and I started out with all kinds of dishes, cookware, folding chairs, portable tables, etc. Most of the time I just hauled it around and did not use it. We gradually unloaded the stuff we didn't need and got by just fine.
If you start with a short trip, make note of things you didn't use and well as things you SHOULD have taken and go from there. Obviously all campers are different but you will learn from your own experience what you will need.
Mainly, just relax and enjoy your new RV. You will meet some great folks along the way. Good luck.