[rdiddly]

It's not exactly a guiding principle, just more of an analysis & learning technique: Get ahold of a big piece of drafting paper, or a whiteboard, or one of those big-ass pads of paper they're always putting on an easel for silly brainstorming sessions. Something physical, big, writable, and not a computer. Set it up or pin it up or tape it up, semi-permanently, and use it daily to diagram and map out each new thing you learn about the system and its interrelationships. I'm assuming here that you have the space to set something like that up. If you don't, you're in a 3rd world programming situation and you have my sympathies, but you can always do something graphical within the computer, too, especially if you have a big screen or multiple screens. I just have always found it quicker to do it in a physical medium.