A useful post from CFAR co-founder Andrew Critch's personal blog describes how to get the most out of graduate school -- especially if you want to maximize your positive impact on the world.
Sample tip (this is 1 of 8):
Find a flexible program. PhD programs in mathematics, statistics, philosophy, and theoretical computer science tend to give you a great deal of free time and flexibility, provided you can pass the various qualifying exams without too much studying. By contrast, sciences like biology and chemistry can require time-consuming laboratory work that you can’t always speed through by being clever.
Read more: http://acritch.com/deliberate-grad-school/