Recently, one of the phrases filling my mind is "selection and focus."
I often think about this concept during the depiction phase of linework or coloring.
It’s about deciding which parts will be depicted lightly and where to concentrate detail.
For instance, in this painting, the areas of focus for depiction would be Sekoshi's face, hair texture, reflected light near the skin contours, and the pattern of tiles in the background.
Even within those areas, there are further layers of detail—for example, within the face, the eyes; within the hair, the darker parts, and so on.
Deciding which parts to depict in detail and which to simplify depends on your intention.
The reason for emphasizing the face is that Sekoshi's embarrassed expression is the main theme, while highlighting the tiles in the background balances the overall composition by drawing attention to the opposite side of Sekoshi's face.