“Every painting, even complicated ones, has a foundation that is built upon simplified shapes. Yet this isn’t necessarily what we see first. We are distracted by a sea of details, colors, and narrative content. To simplify we have to see through all the layers of complexity and busyness. …
“As representational painters, it’s easy to think that completing a picture means adding more information. In fact, the opposite is usually the case. Our goal isn’t to include everything we see, but to know what to leave out.”Mitchell Albala, Shape Interpretation
To leave out or not to leave out, that is the question. One way to learn is to do multiple versions of the same painting, each time reducing the amount of detail. This could be done focusing on the number of elements, the amount of information in each element, the size of brushstrokes (getting bigger not smaller!), the number of brushstrokes.
Play a game with yourself in which you’re allowed a specific number of brushstrokes, say 50. (You don’t want so many you get caught up in the counting rather than painting.) The the next version you’ve got 25. Then 10. What is the essence of the scene, what’s fundamental that you want to include. Perhaps start with a monochrome painting, eliminating the distraction /complication of colour.