Look beyond the hard-edged darks in this floral display to see what was there before the final layer was applied. I think the paper was mostly wet, which allowed the green and purple and brown to flow together. The purple patches in the center area were all one shape. As the paper dried the large shadow (bottom left) was painted, giving hard edges to some of the individual flowers and the sunlit portion of the vase.
Looking at the center portion of the bouquet you can see that it didn't take much to show what all that color was about. Just a few dark strokes on the now dry paper were enough to establish the separate components of the subject.
During the early stages of a painting it is often appropriate to put the emphasis on what the various shapes have in common rather than how they are different.
Here's another Chisnesian painting to consider
If we zoom in, you can see that much of the group of buildings has been initially treated as all one shape. Some whites were reserved, but most of the shapes have in common that they are in shadow. The artist is focussing on how the shapes are the same first, then shifting emphasis to how they are different. The progression is from general to specific.
The following images are good candidates for painting in this manner. Make a couple of sketches first, exaggerating the sameness of adjacent shapes. Then see what you can do with the hard edged darks. The idea is to gain confidence that the layers that come later will provide sufficient opportunity to clarify the content. Take care not to over do the hard edges. Better to err on the side of too general than too specific.