Here is my thumbnail, and what this does, is it establishes a design for the painting. I was most happy with the triangle of dark vs. the opposite triange of light, so this was the only thumbnail I did. I usually do 2-3 until I get a layout I'm happy with. If you can't see a good painting in your thumbnail you won't see one on your canvas, so it is an important step for me. Besides the design of the painting, I also use the pencil sketch to establish the values--don't worry about detail, squint your eyes, (man, there were some funny looks at me when I was squinting as the people passed by) this lets all the tones group into large patterns (shapes) and only draw SHAPES, just SHAPES of tone. I constantly use this thumbnail as my guide as I paint, it was right beside my water container as you can see by the splashes. I look at it and say to myself, "no, all the colours in that area are dark" or "no, all the colours are middle", you get the idea. Otherwise I could slip-up and with a quick look put values in the wrong places.
Hopefully, one more picture to come
I had a friend walk by who snapped a picture of me working-- he took it with his cell phone and was going to email it to me so I could post it...if I get it I'll post it. So check back in a day or so.
Please comment, I really enjoy everyone's input.