Environment looks dull

I am working on a Car Racing Game for Mobile Devices and I bought a few maps from the asset store but the map is looking very dull. What should I do to make the map beautiful and more realistic?

Note: The game is for mobile devices so adding too many trees will be a bad idea as it will drop the FPS.

I AM A PROGRAMMER NOT A DESIGNER SO PLEASE TELL ME THE EASY WAYS.

Thanks

There’s no one-fits-all solution, look into post-processing and shaders

edit: ow that you posted an image basically all i can say is if you want to have a good looking game you need good looking assets. the ones you got there are pretty low quality and, even with post processing and shaders, you know how the saying goes “even if you polish a turd, in the end it will still be a turd”

you could add in lots of trees without much performance hit depending on how you do it.