Once I finish the thumbnail sketches, I then proceed to the final preliminary drawings. This is when I will collect and shoot any needed reference material.
If I stray at all from the original thumbnail concept it is usually very minimal and usually only because of a perspective issue or some other unforeseen element.
This is probably one of the most exciting points of completing an illustration. Details begin to emerge and the pieces start to take on a life of their own.
From this point, there is very little left to the imagination. All the bugs are worked out. My course is set. And I know in pretty complete detail what the final image will look like.
I'm ready to move on to paint.