Lilly recommends the following next steps:
This is all dependent on your interests and what career path you would like to pursue. Generally, Universities will want you to do 2 or so years of general education [History, sciences, math etc..]
For your major courses, these will be more applicable to what degree you will acquire. If you have an interest in say Business, you could pursue Business courses such as Business ethics, Management, economics and so on. If you are interested in Engineering, there is many different branches such as electrical engineering, chemical engineering, or mechanical you could choose from.
Kim's answer regarding any type of logic class is spot on as far as I'm concerned. Also, one that flies under the radar that I really thought was interesting, as well as many of my friends, is a class in linguistics. Understanding the origin story of languages is fascinating. Especially when you see how interconnected so many languages are.
I'd selfishly suggest you take a closer look there :)
Having read Lee Iaccoca - Chrysler/Ford CEO autobiography - he mentioned that even though he was studying Engineering at Lehigh Univ - he was very grateful to take Psychology 101 course where he learned to read people face/expressions to make an informed decision when he was running these two companies.
I also suggest take courses in English writing which will help you in your professional life.
Writing succinctly is an art and not too many people possess this quality.
Lastly, public speaking is very important- if you cannot stand in front of your audience to deliver what you are trying to convey - it is all wasted efforts.