I think there's a lot of areas that can be improved so im going to suggest a few things to look as a first step.
the mountains cliff and hill all have a bright outline id get rid of that. replace it by touching up a few of the edges with highlights where the moon light would be hitting it.
the river and lake look quite unnatural. rivers are never perfectly straight and when they connect to a large body of water they don't have corners.. instead they get wider.
the background mountains could be improved with a little shading
in this example i have dug up from Google you can see the dark triangles of shading? these give the mountains a shape instead of leaving them like a card board cut out.
i am not sure what is going on with your moon? if its supposed to be a smaller moon/ planet in front of it or a hole/socket in it? and also the 'field'? looks like its got corps at least 5 floors high.