Nice work.
One of the most powerful ways to add depth is via overlapping.
Meaning, an object that partially covers another objects.
For example:

In your case, if you draw the cast shadows of your objects, some objects can overlap these shadows, and you will get a sense of depth.
Composition is how you arrange things in space, and you did well by arranging them in space, and not in a line.
I think you can do very good with some more practice.
Nice work, and good luck!