Don't be afraid to take the highest level classes in high-school, if you get the chance. In my experience people in higher level honors classes tend to be nicer and more tolerant of individuality. The subject matter may be harder, but homework is often lighter, (and the other students less disruptive) and that gives you more time to study. If your school gives extra weight to honors/AP classes when determining GPA, the decision should be a no-brainer.
Similarly, people in college are genuinely nicer than high school students. Partially, this is just because college students are more mature, and have learned self-control more than high-schoolers. But a big part is the selection effect, the more conscientious/intelligent students are nicer, and they go on to college more often than others. Plus, of course, most college students want to be there. Lots of teenagers see their high schools as being like prisons, and they are resentful. I witnessed kids getting bullied every day in high school. I never saw that in college (and I've spent time in 3 schools, counting grad school). So you can be yourself more at college than in high school: take advantage of this!
I wish I had spent more time as an undergraduate going to parties, drinking, and doing internships/ independent research. I wish I had spent less time studying, surfing the internet, and playing video games with roommates.
I drove around the US with a buddy one summer, visiting national parks and beaches. I wish I had done more of that and not rushed to graduate early.
Majoring in something like history or philosophy is fine but don't bother going to grad school in that subject area (return on investment for M.A. degrees and PhDs are much lower than for BA degrees). Majoring in something where you actually learn useful knowledge or skills (like computer programming or engineering) is only useful if you actually want to work in those fields.
Playing video games with roommates was the best time I had in college. Until said roommates decided that someone else would take my place in the room next year. :(
I actually ended up having a much better time overall in high school than in college.
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.