IphoneX Ilustration

What are the ways you achieve depth in 2D work?

While I was doing this work, I first made the phone's interface, but it seemed empty and uninteresting to me.

What's missing? (I always ask that).
Why is it so static and boring?

I needed to add dynamic and movement.
I put in flywheel avatars to increase repetition and the fact that they float in the air, it also gives the movement. That makes the design very interesting.

Do you encounter problems with reaching depth and in what ways do you manage them?