That's a wonderful question, sorry it took me over a week to notice it and reply.
A lot of the practical debugging happens with debugging tools on the computer but every now and then I run into issues where it's not obvious why something is acting up. Usually in these cases, there's a conceptual issue, maybe a misunderstanding or an assumption that took me the wrong way.
In those cases, I like to start by writing down my understanding and assumptions of the situation: what is the problem, how does it happen (do I really know how to replicate it), what should be happening.
The act of writing it down (which I call a brain dump) helps me organise my thoughts and often that helps me notice the gaps in my knowledge or understanding which activates my brain to think about the missing bits which often leads to revelations.
One time, when I had just started on a legacy project and was struggling to understand how things worked and where the bug was, I printed out many many pages of the code, booked a meeting room for the day, taped the code printouts to the walls of the meeting room and started drawing and annotating.
It helped me see patterns from a birdseye view of the code and see how things related to each other and I eventually found multiple issues that I was able to fix more efficiently at once because I had taken that viewpoint instead of just trying to fix one class or function at a time.
