Yorick, and anyone else who is serious about reducing existential risk and is not in our contact network: please email me. anna at singinst dot org. The reason you should email is that empirically, people seem to make much better decisions about what paths will reduce existential risks when in dialog with others. Improved information here can go a long way.

I'll answer anyway, for the benefit of lurkers (but Yorick, don't believe my overall advice. Email me instead, about your specific strengths and situation):

1. Work on rationality. To help existential risk at all, you need: (a) unusual ability to weigh evidence fairly, in confusing instances and despite the presence of strong emotions; (b) the ability to take far-more evidence seriously on an emotional and action-based level. (But (b) is only an asset after you have formed careful, robust, evidence-based conclusions. If you're as bad a thinker as 95% of the population, acting on far-mode conclusions can be dangerous, and can make your actions worse.)
2. Learn one of: math, physics, programming, or possibly analytic philosophy, because they teach useful habits of thought. Programming is perhaps the most useful of these because it can additionally be used to make money.
3. Learn people skills. Tutoring skills; sales skills; the ability to start and maintain positive conversations with strangers; management skills and experience; social status non-verbals (which one can learn in the pickup community, among other places); observational skills and the ability to understand and make accurate predictions about the people around you; skill at making friends; skill at building effective teams...
4. Learn to track details, to direct your efforts well within complex projects, and to reliably get things done. Exercise regularly, too.