Wow.. This is a very good question, but very difficult for me. I was a very mature teen. I was home schooled, and passionate about studying. I was ready to graduate at 14, but couldn't take the test until I was 18. So I immersed myself in studies of things schools didn't offer. I studied religions, history, needle-arts, nature, etc. I worked, I saved money. I practiced a frugal lifestyle (bought all my stuff second-hand), and I was very close to my family. I am pretty much the same now.
I guess if I could go back to that time, when I really hated and resisted technology because it threatened my family's closeness, I would tell myself to get savvy sooner. Embrace the internet, learn everything possible, because the future would depend on it. If I hadn't been so stubborn, I could have already been successful online, and would have had a much more substantial nest egg.
I would also tell myself to buy up all the bell-bottoms that came out then and hoard them for the skinny-jean re-emergence!