As a rule of balance with black and white, try to hit a composition that is around 50% black and 50% in the back of your head. That will help decide how dark things should be. You might want to do some wallpaper design for the wall in the background, and adding slight indications that light his hitting the glass on the window by placing some darks on the actual glass.

As for the crookedness of the table and chair, I honestly don't think its distracting to say the least. If it still bothers you you could try cropping the image slightly, just tilt the paper so you get the angle you want, then cut new straight edges. Doesn't take much, so don't overdo it Though if you do that, you'll slant everything else in the drawing XD.

I'm terribly sorry it took so long to reply, and I hope that you this in time before you finish, it's looking great . Blood!