Howard Pyle (1853-1911) was the father of American illustration. His powerful compositions (such as these horizontal stripes across a background color field)...
In some of Pyle's sketches we see him carefully mapping the placement of figures and objects in space:
But my favorites are the ones where we see Pyle wrestling with the abstract designs of his paintings:
Delaware Art Museum which owns a treasure trove of Pyle's sketchbooks showing the master at work (Thanks, Mary and Erin!)