The Velvet Revolvers

[Bookend]

Book: Yep, what Olooriel said. :) It's easier to see how elements relate to the entire comp when you can view them as flat masses. So I would suggest you block in the entire form, not just outlines.
You can do it with linework of course, but I feel you aren't able to truly judge the comp without seeing the value masses as they will be.
In terms of thumbnail tips, be very wary of bisecting your canvas equally, that tends to create very static compositions. Think overall about your lights and your darks. You can actually boil down much of the strength of any composition to the basic two value arrangement of lights and darks.

All right, thanks for clarifying.  I understand now what you mean. I'll go in and try this 'blocking method' with future studies and see where I end up.

Thanks for your thoughts about thumbnails.  Also very helpful.