Early Stages - I try not to think too hard in the early stages. The goal is to just "do", and really, anything will "do". However, I was thinking about mixing a lot of opaque grays and tried to keep them light (in value). They came out a little darker than expected. The early stages can be several layers of paint applied to the surface.
Here is a closeup/detail of some deep scratches in the surface of the board.
Middle Stages - Putting in the dark black curve (lower right) and sanding down a large upper layer of opaque white did a few things that helped this painting move along in the right direction: the lights and darks were now pretty visible and straightforward. A lot happens during the middle stages, i.e., paint is applied, dried, sanded, scraped, reapplied, dried, sanded, scraped, yup, this goes on for a while.
Last Stages - Within the light areas and the dark areas it's nice when there's something interesting to look at that is different and varied, but not too contrasted as to take away from the overall value pattern. It is always a question of nuances vs. direct hits that are more aggressive.