When you look at your painting subject with an eye toward where to begin, it is tremendously helpful to be able to see right through the darks and middle values to the lightest tones. The first layer of your painting usually comprises pale washes that describe a very general version of the major shapes.
Ignoring the darks can be tricky. To get that dark layer to hold still long enough for you to "peel it back", it may help to practice seeing it as a separate collection of shapes.
Find a high-contrast image, or use one of those below, and make a simple painting of the pattern made by only the darks. Use a single color, and make all the darks very dark. If a shape seems neither dark nor middle value, decide which it is closer to, and round it up or down. We're simplifying here, so some compromise is required.
A benefit of getting good at seeing the darks as a separate layer is that you can look at an image or a scene and "read" how much of the narrative content is carried by the darks. If the darks alone tell most of the story, that means you can be carefree in your treatment of the layers that come before the darks. Stay tuned for more about this...