Most people in the US with internet connections who are reading this site will at some point in their lives graduate high school. I haven't yet, and it seems like what I do afterwards will have a pretty big effect on the rest of my life.*

Given that, I think I should ask for some advice.

Generally,
Any advice? Anything you wish you knew? Disagreement with the premise? (If you disagree, please explain what to do anyway.)

More specific to the site,
Any advice for high schoolers with a rationalist and singularitarian bent? Who are probably looking at going to college?
Anything particularly effective for working against existential risk?
Any fields particularly useful for rationalists to know?
Any fields in which rationalists would be particularly helpful?

This is intended to be a pretty general reference for life advice for the young ones among us. With a college selection bent, probably. If you're in high school and have a specific situation that you want help with/advice for, please reply to this post with that. I think that a most people have specific skills/background they could leverage, so a one-size-fits all approach seems to be somewhat simplistic.

*I understand that I can always change plans later, but there are many many things that seem to require some level of commitment, like college.

Edit:
As Unnamed pointed out, also look at this article about undergraduate course selection.