1 - Precisely establish your visual target (which art style you are aiming for + the technical specifications of it). This is usually done by looking at existing titles. 2 - emulate that target.
Your blacks are too black, your whites are too white, and if you are building this for mobile you need to think much bigger when it comes to small details. A lot of the smaller things you have painted are just going to be lost if the final model is only an inch or less on your screen. All of those red safety triangle you…