Give animation a job
Motion can show that a menu opened, an item moved, or a new panel appeared. If it does not help explain a change, it may be visual noise.
Keep feedback close to the control that caused it so the result feels connected to the action.
Keep it quick and restrained
Prefer small opacity and position changes over large, continuous movement. Avoid animating layout-heavy properties when a transform can create the same effect.
Test on a slower phone as well as a desktop. A polished transition should not delay access to the content.
Respect reduced motion
Use the prefers-reduced-motion media query to remove or shorten non-essential movement. Keep the final state and all information available when motion is reduced.
Animation should enhance the interface without becoming a requirement for understanding it.