Avoid riding at night - it's hard for cars to see you, and that's when the drunks come out.
Use lights and reflectors if you do ride at night, and avoid busy roads where cars travel at high speeds - if you can.
Hydrate. And learn about eating on long rides, else you'll be in big trouble.
Don't overdo it.
Join a bike club.
Don't always ride at the same speed - after your fitness level improves a bit, keep pushing the speed. There are lots of posts here about training.