These days, I am trying to figure out the global picture of my phd, that's why I am into napkin sketches and mind maps. I found this short tutorial on the web. Here are the rules:

Mind mapping (or concept mapping) involves writing down a central idea and thinking up new and related ideas which radiate out from the centre. By focussing on key ideas written down in your own words, and then looking for branches out and connections between the ideas, you are mapping knowledge in a manner which will help you understand and remember new information.

- Use lines, colours, arrows, branches or some other way of showing connections between the ideas generated on your mind map. These relationships may be important in you understanding new information or in constructing a structured essay plan. - Draw quickly on unlined paper without pausing, judging or editing - Use capitals to encourage you to get down only the key points. Capitals are also easier to read in a diagram. - Put main idea in the centre, landscape style - Leave lots of space: some of the most useful mind maps are those which are added to over a period of time