Well, I could borrow plenty of books and start working it out for myself, which I have to do with a lot of other stuff anyway. But instead I found a great lecture series on YouTube from Stanford.
Online lectures are one way to keep my study practices varied and it will also save me a lot of time. The lecturers are generally very experienced and entertaining (they give me good ideas for my own presentations).
If, like me, there are subjects you need to upgrade your background knowledge, check out the many online lecture series, from fantastic universities all around the world.
Here are a few of my favourites:
You can find more, on hundreds of topics, at open culture.