Not sure if this is "obvious" or not, but a very simple thing I've been doing for the past 15 years is to write a short log entry every time I encounter an especially tricky bug.

I've found this to be a really good way to learn from bugs. There is something in the act of writing it down that makes the lessons of it stick better in my mind.

More details here: https://henrikwarne.com/2016/06/16/18-lessons-from-13-years-...