Here are a couple of images that resolve neatly into light, middle and dark layers. There are often multiple layers of the middle values, as is the case here. Notice the clouds have a horizontal band of shadow that is darker than the overall cloud shape. The water fits into this category, too. It is darker than the cloud, but definitely not as dark as the trees.
If you are feeling brave, try to match the edges you see in the photo. Otherwise, let the paint dry between layers.
Which is lighter, the boat or the clouds? Squint hard to see which shape emerges. When you get to the darkest darks, let the shapes have some color identity. Just because it's dark doesn't mean it has to be black.
You can desaturate an image to better read the values.