Here's an image that could progress very simply from light to dark and from general to specific.
What should you do first? Then what? Is there anything you should do while the first layer is still wet? Is there anything that you should reserve? These are the kinds of questions you might need to answer in advance.
Having at least a rough idea of the sequence of washes and strokes can make the painting process much simpler. For example, seeing this image for the first time you might be most attracted to the beautiful trees.
It could seem natural to paint them first, until you discover how tricky it is to paint what's in between them.
Planning ahead needn't always be a complicated process. It can reveal a way to simplify a painting that at first seems very complicated. Here's a scene that invites just a little planning. You might benefit greatly from a very simple road map:
Light, middle, dark.
Have some fun with these. Maybe try painting one without a plan. Just dive in and see what happens.