I remember reading various musings on the fact that lesswrong keeps reinventing the wheel or not bringing in enough outside ideas, and I happen to think I have some that are worth at least considering/looking into.
I have done cursory searches for them using this site's search, so as not to duplicate someone else while being unaware of it. If there is in fact coverage of these that I didn't find, please let me know in the comments.
BetterExplained - a site that explains math and some other stuff, and seeks to produce really good explanations of things, and has an interesting model for how to approach making explanations. (This would be so great if combined with a hypothetical functioning Arbital!)
Master of Memory - mnemonics, the kind Brienne already talked about, but with practice problems and specifics, and a full Spanish course, (apparently.) I do not know the actual quality of this course, but the fact that I already memorised three phone numbers (in a minute each), and also a few poems and a paragraph of text, suggests that mnemonics is at least somewhat effective as an approach to learning. Things to explore on that website - the startup guide and then the other methods (some are not covered in the startup guide) and then possibly the podcast.
There's a Russian methodology called TRIZ - the acronym might be changed up to be TRIP, expanding to Theory of the Resolution of Inventor Problems (wikipedia suggests Theory of Inventive Problem Solving instead). It's a very systematic way of approaching problem solving. I'm learning it at the moment, and I might be able to do a post describing the basics of it soon. Meanwhile, there's a wikipedia page. It doesn't seem to be entirely consistent with the things I'm learning, but I am well aware that I just began.
Thank You For Arguing - a book on persuasion/rhetoric, somewhat more systematic than other persuasion things I've encountered, advocates redefining words your opponent uses in one chapter (which led to amusing mental images of consternated my-model-of-rationalist-adjacents), but this chapter can be skipped and the book otherwise contains very interesting advice, some of which I've installed TAPs to apply. I think they work but success rates on social stuff are really hard to measure.
I do not commit to anything because I've seriously tried committing and it just made me stressed and did not result in what it was supposed to result in. That said, I might come up with more ideas to suggest or I might do more in depth summaries of these.