The idea is to take advantage of seeing in advance when it is time to make sure the viewer can recognize what they're looking at. That knowledge keeps you from becoming specific prematurely.
We have seen that looking at the dark layer by itself often reveals whether those darks are responsible for defining the content of the painting. Sometimes you can see the role the darks play without even making a quick preliminary study.
Merely squinting at the scene, above, makes it clear that the darks alone could describe the narrative of this image. Everything is outlined in dark colors! The green, the orange, the grey and even the blue
could be blocked in very approximately and those darks would still pull the whole scene together.
If the image or scene you are interested in painting does not readily reveal the role of the darks, make a study of just the strong darks. If the study can be easily understood even without any of the light shapes or the middle values, then it must be the darks that are providing the content. If, on the other hand, the darks by themselves leave space and light ambiguous, it must be that the earlier layers play some part in establishing the identity of the shapes. That means you have to be careful at an earlier stage of the process.
Using the image you brought home from class, or one of these attached to this post, assess the role the darks play in telling the story. If you can do that without making a study, good for you. If not, please keep the study to 15 minutes or less.
Make a painting that takes advantage of what you learned about the role of the darks. When you have a chance to be carefree, let the paint go outside the lines. The goal is UNDERSTANDING, not pretty pictures.
The smudge in the upper right is my finger, not exactly a major shape.