These are my preliminaries and thumbs for the final digital paintg which is here
I chose the chapter of the book called Champion and Chief.Unfortunately Dejah Thoris is nothing more than something to save in the first book. I thought about having her in a fighting stance (early thumbs) but changed back to the description.
The process is, sketches out of my head and thumbs first. Then I use a mirror to refine them and shoot reference for a more accurate pose. In the case of the thark head I made a little 2 inch clay model of the head for reference. The background is from my ref and a max model I built to help with my visualization. I then scan the pencils and combine them in layers in PS and then move things and change them as I refine them and problems crop up that forces me to deviate from the initial thumbs.