When I was 18 I was just about to go off to college. I had come from a pretty shitty family and in many ways was already pretty independent. My one and only goal on my mind was "get out" and do whatever you have to do to achieve it. And I did. But id be lying if I said I was much happier. Granted, Im only 25, but Ive been around the block enough where I think I can give you some good advice
1) Don't go to college. The debt isn't worth it. When I was attending the costs of colleges just started soaring and the interests rates started rising. Not worth it. See if you can cheat the system by working and going to school part time and not incurring any debt. Despite what people will tell you, the debt isn't worth it, the higher salary you will make will not offset the loans.
2) Go out and have fun. I am glad I made friends who were a bad influence, because they really showed me how to have fun. Lots of good memories.
3) Broaden your experiences. Seriously, trying everything. If it sucks, no big deal, just write it off and move on. The more things you try the more information you have about yourself, and thus you will be able to make better decisions about what you want to do with your life.
4) But, if you are already sure what you want to do, throw everything at it. Be proactive, take chances, set your self up for success!
5) Learn about investing and financial management. See, my parents were too busy cursing me out or fighting with each other to help my sister and I prepare for life so we had a late start in this respect. When I got out on my own I quickly learned to save, never get a credit card, and think ahead. Don't buy anything you cant afford up front in cash.
6) Ironic to my point #5, appreciate the adults in your life who will help you and want to succeed. What I would give to have had a father that would have sat down with me to teach me things, or a mom who wasn't too sick to spend time with an learn from her. To this day it is still painful to think about how life would have turned out if there was a consistent positive roll model in my youth and early adulthood to help me when I get stuck or make a mistake. Take advantage of your elders advice. Seriously. And appreciate the people who care about you. Their help will be invaluable to your success. Take a look at Richard Feynman's remarks about the influence his father had on him studying physics, for example.