I’ve learned a lot from this discussion. I really liked @maxo’s sketch. For fun, here is one I’ve just finished up. It represents the Javascript Object class, an abstract structure with many small moving parts. This is mostly ‘mature’ knowledge. I know this entity and I’ve used most of it’s amenities but I waste a lot of time checking details and sometimes have failed to use options simply because I forgot they were available.
It is very densely packed even at a glance. The chambers are packed together and stuffed with information. Each one of those legends will get its own little sketch where it’s details are encoded. There has been some discussion about the separation of memory chambers. This is very important. The traditional advice, according to @RMBittner is to put large distance separations between them. Here I have given each room a character or a theme. The Lock chamber is for access control. The basket for all the ‘get’ methods and the snake keeps all the ‘is’ methods ( hissss to you too!) This provides enough distinction for me. Alligators are prototypes and stone buildings have to do with ‘objects’
In this case, as I said, I knew the material and had a good plan for organizing it. Sometimes with new material, I find after a while that my little ‘scene’ is not the best representation and I redraw it. All of this provides very strong reinforcement of the material.
It’s important that I enjoy this. I get to be a teenager again and play with dragons, gold. I have a stories about it. It’s rather personal. It’s important that it be so, but I wouldn’t show you all my sketches 
I think color would be a real advantage but I don’t want color in my drawings. You can do cartoons, stick figures, copy & paste clip art - the style or the level of technique is not important except that you should enjoy looking at it.
If you haven’t tried this kind of technique, you may find at first that it’s a lot of work and you want to throw the results away. Be patient. You get a feel for it over time.
This time the gray scale came out a bit too black. It’s not as harsh as this photo. Still learning
