Well... I had to do pristeen16 cover #2 in a hurry last week for Previews... so I'm gonna redraw it tonight. I often redraw things 3 or 4 times.
I start with a thumbnail (about 4 by 5 cm) and scan it.
Blow it up to fit an IDW page, and tinker in Pshop.
Then I print A3 size, mix a martini, and draw under the influence with a 5B pencil.
A great piece of advice I got years ago from an Animation director was to look at your picture as a silhouette. It should hopefully look dynamic and understandable like that.
Well... anyway...martini time (In the interests of work you understand.)