Some painting subjects translate readily into the washes and strokes of watercolor. The cast shadow of a telephone pole, for example, might want to be clean and simple: a single stroke, with no texture. The shadow of a tree, however, might involve hard and soft edges, lacy dappling of lights and darks, a warm glow around the cool strokes...
Such complexity can lead to all kinds of trouble. Simplification seems to be the order of the day, but how do you know what to include and what to let go of? Experience helps, of course. You can riffle through your mental Rolodex till you find "Tree shadow/dappled sun", and use your tried and true approach. The thing about experience, though, is that it takes so long to get.
There are a few things you can do right away. First, flip the switch from "Content" to "Form". Look at your subject as shapes, patterns, colors, warm/cool, dark/light, instead of seeing it as subject matter.
Let's simplify this scene by rounding off the number of values to just three: light, middle and dark. If we started by calling the white paper the light, the first layer would be the middle value shapes. Asking a few questions about form will provide simple guidelines for making the pattern of those middle value marks:
What percentage of the page is middle value?
How are the middle value shapes distributed on the page?
What kind of shapes are they?
Proportion, Distribution, Pattern.
What were the answers you came up with? Those are the instructions for how to paint the first layer. Try using the same questions for the darks.
If you made a quick study using this approach, you would not need to shift into Content Mode at all. Your treatment would be abstract. Then you could assess the result to see where you would like more subtlety or specificity, and embellish till you are satisfied.
Look for a subject that seems too complicated (it shouldn't be hard to come up with one), and give it a try.