The best technique I've ever used to learn something is dead simple: I always assume I don't know anything about it.
It doesn't matter if it's brand new to me (like when I started to learn about the stock market) or I've been working with it for literal decades (like when I'm reading about a new software development framework). I go into every source of information assuming whoever wrote it is an expert, and I am their newest student.
I always learn something when I do this. It may not be the most mind-blowing thing I've ever learned, but it's something. I can walk away having created one new dot.
It may also reinforce something I previously learned. This is great too since it reinforces an idea I previously had and points out that, hey, I may have actually known what I was talking about beforehand.
There's always something for you to learn. What did you learn from the last thing you read?