Not bad!
I'm not coming from a know-it-all's POV, but I can hopefully give some thoughts and advice:
1.) The shadow under the table should probably be a little more linearly-shaped, to match the table. I think you were going for a textured look, but got a little carried away, which warped the physical shape of the shadow cast by the light hitting the table. Squinting your eyes, it doesn't look too bad, but when you focus in on the details, it's harder to sell. The shadow has a few dips and rises: to justify this, it would imply that the table itself wasn't straight-edged.
I find the best way to make texture apparent is to use it on the edge of the shadow, and not really at all on the inside, which would imply there are holes in the table that are letting light through to break up the shadow. See that good-sized blotch of brown in the shadow by her knee? I would make that a much darker shade, or just change it entirely to the shadow color... either way, try to make those blotches more-closely matching the shadow area, because--if you were shown nothing but the shadow and not the table--you might assume that the table the shadow belongs to had a hole there.
The take away: Try to make shadows more faithfully mimic the shape of the object they belong to. :) Texture edges before the inside, if you texture the inside at all, which I don't really do, unless very lightly. (A note: In darkness, you will find less contrast between values, hues, chromas, etc. This means that extra care is required when trying to pick out a color in darkness, as a little change goes a LOOOONG way.
2.) The table itself looks is a little thin: it looks like perhaps it has the thickness of plywood, so I would say to double or triple its thickness. :)
3.) Her elbow doesn't seem to be fully (if at all) resting on the table. Out of curiosity, did you start building the character without a plan, or did you start with a pose made up of simple shapes to get the proportions figured out first? If you plot the point where you want her elbow to rest on the table, then you have a first piece figured out of a "pose puzzle", if you will. At any level of expertise, I completely recommend looking into "art anatomy proportions" for constructive purposes. :) There are some great books out there, especially Andrew Loomis' "Figure Drawing for All it's Worth", but look around on the Internet for other sources too.
I could go on about some other stuff, but I'll instead recommend another resource that will explain concepts way better than I: CTRLPaint.com. :) Do check it out, there are a ton of free, informative videos.
Cheers,
-WW