Reading "Diaminds" holds the promise to be on the track of making me a better rationalist, but so far I cannot say that with certainty, I'm only at the second chapter (source: recommendation here on LW, also the first chapter is dedicated to explaining the methodology, and the authors seem to be good rationalists, very aware of all the involved bias).
Also "dual n-back training" via dedicated software improves short term memory, which seems to have a direct impact on our fluid intelligence (source: vaguely remembered discussion here on LW, plus the bulletproofexec blog).
r/Fitness does a weekly "Moronic Monday", a judgment-free thread where people can ask questions that they would ordinarily feel embarrassed for not knowing the answer to. I thought this seemed like a useful thing to have here - after all, the concepts discussed on LessWrong are probably at least a little harder to grasp than those of weightlifting. Plus, I have a few stupid questions of my own, so it doesn't seem unreasonable that other people might as well.