My eBay drawings always start with a loose scribble sketch. I go over the sketch with marker to figure out the linework.
Next I get out my lightbox and trace those lines onto the final page.
Then I start making decisions about anatomy and perspective, changing the base linework where necessary. It's usually about this time that I decide on which character it'll be.
Each drawing takes about 2 hrs, give or take 30 mins.