Whenever I'm in arm's reach of paper and pen I'll probably be doodling: A lot of my best pictures started that way, one little scribble hidden amongst others that I ran with until a finished work emerged. Somehow all of my work starts with a quick sketch, just an outline, rough layout, in pencil or biro. I keep several sketchbooks of various sizes for that purpose. I especially like to work on lightly coloured paper with pencil or biro and a white gel-pen. Also more recently having aquired a Wacom tablet I'm sketching more and more using Photoshop either directly or playing with stuff scanned from my trad sketchbooks.