Here's my process of creating my illustration "momentum:"
I scanned in the thumbnail and printed it out larger. Then I worked roughly over that in pencil, refining and moving things. On top of that pencil work, I refined more with pen and made some more decisions. If you notice the boy's legs in the foreground I decided his position was too placid and my little pushing gesture is at the bottom.
I then worked on top of that with tracing paper to move things around and draw even more refined again.
After I scanned that in, I could move or shrink things with Photoshop instead of redrawing the entire boy smaller, for example. The changes here from the previous one are that I shrunk and moved the boy, and I tipped the swing and shortened the ropes.
And finally when I print that out, I can carefully draw the final line drawing exactly how I want it on another piece of tracing paper on top.
I scan the final line drawing and first do color testing with Photoshop--quick coloring in of areas with flat color and making color adjustments. Finally I make swatches of all colors to sample from for the final, then erase this temporary sloppy color.
I fill in each element by selecting an area one by one and "cutting" and "pasting in" different scanned fabrics.