Welcome to the terrain board!
You could start, in terms of improvement, by not ever using the standard wc3 trees in
terrain art, they sometimes work with playable maps, but never with terrain art.
Other than that you could also probably thin out the fog, and maybe change it from
orange to something a little more... Natural, and then, if you want to give the terrain
a dusk/dawn-ish feeling you could use the "Glow" doodad to add such features.
I suggest you read the lighting technique tutorials, you'll find them listed in the
"A Guideline to Terraining and the Hives Terraining Section" thread, stickied here
in the Terrain Board.