The experience of studying animation — specifically the principles laid out in the Disney era and codified in 'The Illusion of Life' by Thomas and Johnston — has improved my still illustration work in unexpected ways.

The principle that transferred most directly: squash and stretch. In still illustration this means understanding that living forms are elastic and show the memory of forces applied to them. A figure that has just landed from a jump is compressed slightly. A figure in rapid motion has overlapping parts that are slightly behind the direction of movement.

Anticipation: in animation this is the preparation motion before the main action. In still illustration it translates to a poseable moment that implies the action that's about to happen. A character about to throw a punch who is wound up and leaning back reads dynamically because the anticipation is visible.

Follow-through and overlapping action: in still illustration this means secondary elements (hair, loose clothing, jewelry) should be shown slightly behind or displaced from the main action direction, as if they're following the primary motion. This small detail adds enormous dynamism to poses.