Read stuff you have read before
I dunno if you have experienced this in the past, but I know I have. It's a very curious thing indeed; Have you ever read something about technology or whatever field you are in, a month after you did so originally, and suddenly a lot of stuff makes a ton more sense?
So my very clear reasoning for this is, you study something, OK got it, later when you study it again it's much clearer and obvious and you can think in it much better because now you have experience/more knowledge to link it to. So before it was a stray piece of info, now it's clear how it interacts with everything. Or something along those lines.
So anyway, read stuff you've read before, as long as you've learned other stuff of the same subject or you have been working with the same subject, stuff will make more sense and will be clearer in your head.