Alrighty, the first thing I would have to say, is the scene you depict looks highly unnatural. So you have a few mapmodels of trees scattered around, that doesn't really help the fact the geometry is flat, and is this rectangular block floating in mid air for some unknown reason :P
The lighting does not make the scene come alive, as the shadows it is casting don't really mesh with the skybox you've used. Maybe you want this to be a night time map, stick a moon mapmodel up in the sky and light the map using that. You could get some excellent shadows that way, but before you do this, follow my first paragraph and fix the geometry to be more life like.
Next, think about continuity, where is that lava going, and where is it coming from? Why does it just stop at the edge of the rectangle? Try to depict a believable world, and note this does not mean I am saying make it look more realistic, because that is not the point of a fantasy environment, is it?
Anyway, keep going, and improving this as much as you can for as long as you can. Maps take a few hours to make, masterpieces can take forever.
