To simplify something as complex as a rocky outcropping, it sometimes helps to think in terms of groups of planes.
In the case of these rocks along the coast of Maine, the rock naturally breaks into four fracture planes:
1. Top planes
2. Side planes in light
3. Front planes in halftone
4. Side planes in shadow
The actual scene had a lot more complexity of form and randomness of tones, but if you group the planes, it will be easier for the viewer to sort things out, and the form will carry more punch.
By the way, this was painted with a very limited palette: Black, white, burnt sienna, and yellow ochre. An ultra simple palette was enough for a pure form study.
When you're painting details of a larger scene, like these small figures in a Canaletto painting, you can simplify planes to light, halftone, and shadow. This makes the details read instantly, and it saves painting time.