How you translate a subject into shapes of just the "right" colors and values is largely a matter of setting aside what the content of the scene means to you, and looking strictly at form. A white house in shadow, for example, is not white, but thinking of it as "a white house" can confuse the process of deciding how to paint it. When we shift our attention to observing form, we are stepping into the realm of the abstract, where form is simply form, and the eye overrules the mind.
This can be a slippery process, since understanding the meaning of what we observe is a basic survival instinct. Keeping your vision abstract involves deliberately changing channels. T make it easier, try asking these questions of whatever part of the scene you are about to paint. With your brush loaded and ready to apply a new layer, ask about:
Proportion: What percentage of the overall shape is the new color? 20%? 40%? A little more than half?
This is a very general way of looking at a subject, on a par with, "what color do I need?"
Distribution: How is the new color distributed throughout the overall shape? Is it regularly spaced? Concentrated in certain areas? Always in predictable locations? Random?
Pattern: What kind of marks will be appropriate? Rectilinear? Organic? Vertical? Diagonal? Are they connected? Separate? Square? Round?
The answers to questions like these are abstract qualities. They progress from general observations toward more specific ones, but they do not require checking to see if you are making a good version of the subject. A fair amount of faith is involved in believing that your observation of purely formal aspects of the scene will result in a reasonable interpretation of the content. Can it really be true that knowing that your marks need to be horizontal, roughly rectangular, and cover about 75% of the big shape will be enough to tell the story?
In fact, as painters we ask this kind of question all the time. Before your brush touches the paper, we are used to asking what color we need, how dark, and how wet the brush and the paper are. These are abstract questions, too. Here we are just extending the familiar process to include how the brush should behave.
The image below is made up of a just a few major shapes - Water, yellow-green banks, forest. For each one, try asking the questions outlined above.
Now choose an image of your own, and make a painting that proceeds entirely on the faith that pure form will get the job done. When you get to the stage of making small dark strokes, stop. Set the picture up on the table, or pin it to the wall and stand as far back as you can get. What do you think? If it tells the story, you have made a realist image without ever becoming specific. This may have enormous repercussions, or it may just shake things up a little. In any case, it should serve to remind you that with watercolor, it is not only possible, but also wise to stay abstract as long as possible. Given our common tendency to get specific prematurely, this is important news.