When I come back to the painting, after allowing the last layer to dry, I double check placement and proportions and the relative values. I make note of how the colors are working, what areas need to be greyed and pushed back, and where I want to boost the light and color to draw the eye. I spend as long as it takes to get these fundamentals working with my vision for the piece. Then I start in on the smaller details, the rounding of all the individual cylindrical shapes and then all those pesky spines and their shadows.
The completed painting is at the top of the post.