Looking back on my 64 years of photography, there's two traits I wish I had had when I started out -- patience and an obsessive-compulsive disorder.
Patience is a tough one when you're young, but taking your time with composition and waiting for the right light can have great rewards.
The OCD includes, as other have mentioned, documenting, dating and cataloging everything you shoot as well as developing a storage method that you'll be comfortable using all your life. It also means learning and following the darkroom cleanliness discipline, and, again, patience.
And always carry a camera. What kind is almost irrelevant.