The following notes are from a book called : Elements of Design: Rowena Reed Kostellow and the Structure of Visual Relationships . I have copied some pages purely for educational purposes.
Make up to fifty recilinear volumes in clay in a wide variety of shapes. Clay is the best medium because you can both add and take away with relative ease. The edges should read as clearly as possible. Organize the rectangles in groups o f three, keeping these principles in mind.
Appreciate the qualities of contrasting shapes. The volumes you choose should vary in character as much as possible, and no two should have the same measurements. Learn to assess the volume of an element by eye, without measuring.
Establish relationships between the volumes by choosing dominant, subdominant and subordinate forms. The doming volume is the largest element, the most interesting and dramatic in character. It occupies the dominant position in the group. The subdominant complements the dominant in character. Unless there is twenty percent improvement in the character of the dominant when the subdominant relationship can be very exciting due not only to contrast in character but to to position as well. More often than not, the relationship is enhanced if the axes are not parallel.
The subordinate makes the design still more interesting by introducing a third visual element and axis. The subordinate should make the design more three-dimensional, complement the existing forms and complete the unity of the design. It is not as independent as the dominant or subdominant. It should be contrasting but sensitive to the other forms.It must be designed to fill wha is missing in the other two.
Be aware of proportions : overall, inherent and comparative. The inherent proportions refers to the proportions within a form:length to width to thickness.
The comparative proportions are the proportions of one form in relations to another. Think of a tall, thin person compared with a short, stocky one.
The overall proportion refers to the character or overall configuration of a group of forms (If you squint and look at the silhoutted proportions of a group of forms, you're seeing its overall proportions.) No view should be uninteresting in character. In general, in thses experiences, you should exaggerate the vertical in some and the horizontal in others. Most students make a horizontal overall proportion-perhaps because it seems more stable. Never emphasize the cube.