With some rare exceptions that test both, most college courses test either your intelligence or your diligence. A diligence course requires you to memorize material you will never care about and read books you're not interested in. An intelligence course will give you a few models to manipulate or a new type of math to master. If you're good with numbers and what-if scenarios (i.e. supply/demand clicked quickly for you, you enjoyed calculus), then I'd definitely recommend taking intelligence type courses. While your peers spend hours studying, you can read about other subjects you're interested in. If you have the hardware, it's a relatively painless way to slip through one of life's most expensive hoops.
I'm about to graduate with a major in Econ and a minor in math. I'd do it again in a heartbeat. My econ electives were mostly spent on statistics and game theory. Look for classes like those. Stay away from anything with history in the name.
The intelligence/diligence split should be obvious by looking at the class, right?
Why do you say to avoid history?
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.