hills are pillowshaded and completely ignore the direction of the sun. the sun itself has been simplified into a symbol like in children's artwork (no offense). the cloud is flat and also isn't shaded according to the sun. the horizon line is absent. use references of actual landscapes, study famous landscape paintings, lose the frame, and draw from life regularly
All the shapes are too flat I'm afraid. For that matter, when you zoom in, it's obvious some parts (the outline of the hills) have been drawn rather than placed, and the way the cloud blends into the background it looks like it's been tool shaded, so this isn't even pixel art...