I would say there are a few things you can learn that are critical for university and for life in general.
1) Learn to manage your money. The one thing most of us have trouble with transitioning from teen to young adult and up is that we don't know how to live on a budget. I myself am guilty of this. If you plan ahead and stick to a goal and budget you can do so many things like travel, save, etc.
2) Figure out what you want for yourself and who you want to be. It's normal to do things your friends do and to worry about what others think about your choices, but ultimately you have to live with them so don't be afraid to have goal and aspirations and to stick with them. These are your dream and it's your life.
As for Art school, I would take as many little workshops as you can and go to some seminars to see what's out there and who's doing what. You can meet a lot of people new to the industry and veterans and it's a great way to stay on top of trends. Everything come sin time and with practice so do your best and don't be afraid to try new things, art is about thinking outside of the box and diversity :)