Every animation should answer a question the interface just raised.

The question test

Before adding a transition, ask what question it answers. Where did that panel come from? What changed when I clicked? Am I still in the same place? If the motion answers one of those, it has a reason to exist.

If it only exists to look impressive, it belongs in a showreel, not a product.

Durations, not drama

Most interface motion should finish in under half a second. Long animations feel luxurious the first time and hostile the hundredth. The exception is explainer work, where a slower pace can carry meaning.

Choreograph with delay instead of duration. A small stagger often communicates more than a longer curve.