I start with small thumbnails. When I get to a solution I like I scan it in and enlarge it, then print it out. I work directly on that paper until I feel all of the parts of the piece are worked out, and then I line the image on a separate sheet of paper. The lined art is scanned back in and colored digitally. I have found that working this way keeps me from becoming too precious with my thumbnails, but also helps retain the spirit of the original.