Isolate and Squint to See Values
The answer to the age-old question “How do you eat an elephant?” is this: One bite at a time. How do you shade a complicated subject? One little part at a time. Isolate the individual parts of your drawing and see them as shapes with different values.
In spite of the parental admonition that squinting may cause your face to remain in that pose, squinting in art is a rather useful tool. When you squint, edges blur and you are left with lights and darks. Artists know this and often squint at the subjects they are drawing to more clearly see value changes.
Although I’m encouraging you to isolate specific areas and concentrate on the value changes, you’ll need to be sure you look at the entire drawing and adjust ...