I'll leave the construction stuff and get straight to the colouring:
I have quite a pale monitor, but I'd guess that the shading needs to be a lot stronger to stop the whole thing looking flat. You've already got where most of the shadows should be on the figure; they just need to be stronger, particularly on the hair, which is looking pretty scribbly. Figure aside, there should also be shadows* under the steering column, the chair and that ladder's handrail, and more shadow under Leela's foot to show that the heel's raised off the floor. Finally, the background highlights (reflection of the track lighting in the steering column, for example) look too lumpy for a reasonably undamaged surface – perhaps a harder low-opacity brush would help smooth things out.
Best of luck with future artsiness.
* One of many artsy obstacles: the light source can be a git.