Cyangmou hit the points in his edit regarding lighting and composition that I only touched on. It's really all a matter of preference, and it depends on how realistic you're trying to be in your lighting vs. your composition. In my edit, I chose to keep the scene very dark and empty as seemed to be the original intent, and the lighting was very muted, but Cyangmou's lighting draws the eye toward the center more than mine. Mine took into account the light from behind the gate, casting a stronger shadow on the part of the gate you can see, but Cyangmou's preferred visual interest over realism (though if a light were hovering above the ground or so inside the gate over the dirt or an intense light way above in the air, his too could be considered realistic as the light fades more toward the forest compared with the muted ambient light I chose to emphasize in my own edit -- the main difference being, his has a strong focal point, and mine didn't since I was playing off the ambiguous mood I gathered from the original composition, which I thought to be more interesting to me personally). I prefer more muted art for scenery, something with an ambiguity that leaves stuff to the imagination, but Cyangmou's edit has a lot more presence with the intense red sky and focal point, and depending on which mood you were aiming for, you'd use the one that suited your purpose more. The way you'd light the scene and composition would depend on that purpose -- i.e. whether you want a strong focal point or more ambiguity and mystery.
The question is not "how do I light the scene", but rather "what do I want to convey with my image?" You must decide whether you want to be explicit or implicit with your image. Cyangmou's edit (explicit) reads better to an audience because it is clear and direct, and this is usually better for game art or assets with a practical purpose or clear intent to get across to the viewer. On the other hand if you're just establishing a mood or just trying to hint at an idea with no real specific context with your image, a more ambiguous composition like my first edit (implicit) might suit you better (a lot of manga and comic book artists use the implicit composition technique to establish a mood for a scene or show the passing of time).
Regarding lighting and coloring techniques, the actual lighting you had in your original image simply didn't have any clear direction (unlike the lighting in Cyangmou's edit, which shows the light source as coming from the gate/sky area, and he indicates this direction by showing some light reflected off the stump and trees nearest the center of the image, where he assumed the light source to be, and frames the light source with the trees/clouds, emphasizing the omnious mood with the stark red in the sky, which is also mostly framed in the center of the image.)
The only other real problem with your image was that you were over-defining stuff that should be mostly shadow anyhow (I kind of winged it a bit in my 1st edit, but my 2nd was a bit better). Not everything has to be drawn in a dynamic-lighting situation, so keep that in mind to save yourself a lot of work in the future. You're
implying things in shadow, not actually rendering them, so save some time and energy by being vague where you can.
