What I really like about this, apart from the model ;-) , are the tones. I think the colour of the wall and the tone of her skin work very well together. The white blouse and the black hair are great as well.
I like how she is so natural in front of the camera, not seeming to notice the photographer's presence at all, appearing to be thinking about something else entirely, safely in a world of her own.
As you had included the cigarette, maybe it should have been sharp, and some smoke coming out would be a nice addition. Alternatively, you could have left the cigarette out of the pic altogether, and get rid of that ugly ash tray as well.