I'm finding that while i'm working on more 'serious' pieces it works well to have a 'doodle' going on the side. It allows for a break from the need to be really mindful and attentive, as a 'real' piece requires.
These are done on 2.5" x 3.5 (63mm x 89mm) illustration board....using my .13mm Rapidograph. I start with a light pencil drawing (automatic drawing style) and then work over it with my pen. So fun! :)