The first 20 minutes of a drawing is the most critical for me. In that time period, I place the major lines of the composition and roughly sketch in the dark-light pattern. I work all parts of the drawing rather than focusing one one area at a time. If I like what I see, then I will continue with another 20 minutes right after that or later. I don’t work on it again until I know what my next step will be, even if it is only a small step. (This is much the way a writer might stop writing while knowing at least what the next action or bit of dialogue will be. It allows me to start right in without uncertainty or hesitation.)
The second 20 minutes has the most development. The majority of the forms are modeled and adjustments are made where necessary. In the first 20 minutes I worked as much as possible on all parts of the drawing at the same time, but in this stage, I am able to focus more on individual parts because I am confident that the whole is working well. (At times though, I do have to establish again the wholeness of the drawing.)
The final 20 minutes shows the least development because the marks and changes are more subtle. At this point, I am looking to see which portions of the drawing need additional work and refinement. This is particularly true for the lightest light areas and the darkest dark areas which help to give the drawing a focused and finished appearance.
Please check out my main Making Marks On Paper page for a visual table of contents.