Oi a few tips 'cause there's lots that can be approved on this piece.
We have:

- Depth issues
- Too little contrast
- Bad shading/dithering
- Black outlines

To solve these:

- objects in the back are usually darker than objects on the front
- to create some more depth in textures you should up the contrast. Darken the shades, lighten the highlights.
- figure out where the light is coming from (avoid light coming from the front, 'cause that will likely give you pillowshading and that's a big no-no) then follow the objects shape to shade the piece instead of shading each object as one.
- lose the black outlines and use a darker color of the objects color. (a darker blue for the floor for example)

Hope this will help you a bit.