When drawing from observation, it is useful to first sketch the abstract shapes you see and then fill these shapes with form. This approach is also useful for obtaining information from a reference image.
However, when drawing from imagination, it can be helpful to start by sketching three-dimensional forms and then discover the two-dimensional shapes that emerge on the page. A great thing about this approach is that you get to exaggerate the three-dimensional forms. A good design will still look good if you do that a bit.
This is again a Yin and Yang thing, two opposites you can balance. Study reference by studying two-dimensional shapes first, then discover the underlying three-dimensional form and then make it your own; design something new inspired by that reference—and other references—by sketching the three-dimensional forms first and finding the two-dimensional shapes that emerge on the page.
My Morning Sketches APP let you practice both drawing shapes and underlying forms.
Yours sincerely,