Get someone very familiar to help you get the fit of the bike right. A seat too high or too low can cause knee problems. (I am just about over one myself.)
Wear a helmet. Which one is up to you but make sure it fits well. Don't let anyone tell you it doesn't look cool ect, it only takes once. You are going to be going fast enough that hitting the ground isn't going to feel good anyway. Hit it with your head and it can be life altering or life ending. Did you know that until fairly recently Nascar did not require its drivers to wear helmets? It wasn't a requirement until the HANS device became required after the loss of Dale Earnhardt. Yet I don't ever remember seeing a race where a driver didn't wear one.
Also expect the car on the road with you to NOT see you. Yes you are right there and in plain sight, but they are expecting cars and can look right past a bike. Whether you have the right of way or not, car vs bike the car always wins.
Most of all have fun. Use your head and you will find that you notice things you pass right on by in other forms of transport. You will find all your senses are heightened. You will smell the flowers off to the side of the road, or the pig farm just ahead. You will hear the running water of a small stream, and those ride snacks seem to taste that much better beside the road.