Start with your weakest point first, which is lighting the scene. As the others have already mentioned, vertex painting is a great way to add some basic, artistic shading. I call it artistic, because you don't want realistic lighting but a more game design centered lighting setup.
This is platformer and I can identify 4 important parts in your scene:
1. the plattform(ground)
2. the background(wall)
3. the separator(ceiling)
4. important game design features (lift)
The plattform is where the player will move on, therefore it needs a lot of attention. The background isn't important and should be used to help visualising the foreground (=player+ground). The separator should be clearly visible, but should not draw a lot of attention and the important game design features should be like a bonefire. Here are a few steps which might be helpful.
(use almost only vertex paint)
A. Tone down the whole scene:
Tone down the whole scene using vertex color (use a dark,brown tone like #401010).
B. Turn the 3 lantern off.
Turn off the 3 lantern to break the monotomy and to highlight the lift (see below).
C. Pimping the background:
Light up the walls around the left two lantern enough to hint a light fall off on the walls, dont touch the ground yet.
D. Pimp the ground:
Light up the whole ground, use a gradient from the wall (dark) to the foreground(light) and increase the light intensity where lantern are turned on (light fall off). Give the vertex paint a yellow/orange touch where the lights are brightest.
E. Pimp the ceiling:
Light up the ceiling (upper bar) only so much, that a clear constrast between wall and ceiling is visible.
F. Pimp the lift:
First you need to lighten the lift itself, you have a very dark texture, use either more metal to light it up or brighter wood. Then make the two lanterns left and right of the lift much brighter than the rest and use them to light the lift. Best to use a little more color in the light to draw more attentention.
When you watch the scene from the right to the left, the lighting should lead your eyes along the ground and finally to the lift.
My two cent. You scene looks promising and you just to take it to the next leve, try to improve on a single aspect each iteration and you will improve the whole scene really quickly.