These are the major principles behind what makes animations more than just visual polish, and allows them to functionally benefit an experience.
In the world around us objects don't instantly appear. It can be incredibly jarring when this happens in an interface, so we use motion to give context to the appearance of new elements.
It's unnatural for objects to go instantly from a state of movement to being completely stationary. Always use an easing curve on animations to slow down and speed up with movement.
When animating a series of objects consider the order that they should appear in, and how this forms a sequence or hierarchy between each of the individual elements.
Here are a few example animation curves. Linear is put here as a baseline to compare the other curves against.