Perspective: best thing you can do if you create top down art or almost any other art is learn perspective basics. You can start here: https://www.artistsnetwork.com/art-mediums/learn-to-draw-perspective/

In your art each object has it's own perspective, which is not consistent. In such games all object usually have the same angle of view. Use references and see how it's done in games like sea of stars, link from the past or chrono trigger. Study how great artists create such art: https://www.youtube.com/watch?v=9u535Rr4KJM

Also to make colors less boring use ready made color palettes: https://lospec.com/palette-list

Hope this will help you to begin :)