Scribble for a presentation

For this style of illustration, I start with a light grey linedrawing to get the composition/idea approved. Then I make a new layer and make a more accurate drawing on top and delete the initial lines. Then I do what I call "to shit some light on it", which is just adding another layer underneath the drawing for large shadows & accents.
Those drawings need to be finished quickly, which is why I use Flash for doing them. It makes the lines look nice automatically.
In general, the looser the drawing looks the better. The more the client can interpret into it, the better.