blocking in a page

This 60 second drawing is an example of how you want to address the entire page at the start.
You can use a light touch to feel your way around the page and dictate how you want to crop what you see in front of you, turning into a picture on a page.
Quickly define where the shadows will be. You can fine tune later with an eraser and a pencil/charcoal to make the light areas lighter (eraser) and the dark areas darker (pencil/charcoal).