Oh shit that's nice. You've got shapes and shading down, more so than me. What does spring into my eyes is that you should increase the contrast on the skin, to make her shapes stand out more, and perhaps add a few details here and there, if possible. I can see that she's supposed to be pretty (she is!), so you don't need to defile her face with a huge mole or anything like it. =P
Also, i've found that bluish shadows work very well with skin color. Bluish shadows work well with just about anything, really.

...

Also, there's something a bit awkward about her neck. I can't really put my finger on it... Perhaps it's too far back? Maybe it needs to be slanted a bit to the left? Hard to say. Also, her hair makes her head appear really big. Oh yeah, don't forget to shade the shoulders. The shape is good, but they appear flat right now.

That's about it. Very nice job.