scroll: first and foremonst - by improving contrast & coloring
try to capture the materials, even if you stylize try to keep it overall somewhat consistent.
If you are unsure about colors get photo references.
Regarding to color photo references are usually plain bad (if you try to colorpick colors out of the photograph), but they help you at least to get on the right track.
Afterall you anyways want to stick to the big color idea off your picture and you just try to get stuff right looking.
For the mountains and the grass
that's badly oversaturated. THe mountains don't have any perspective or depth and they rather look like cardboard on a stage
look up environment photographs and paintings and learn something about basic perspective and the overall impression will improve greatly.