I think you're doing really well,
I have a few suggestions, use the or don't its your work at the end of the day.
1) I darkened her hair at the bottom to give it more contrast, I feel that curve is important to the whole image.
2) which is why I've also made the neck follow it, I also tilted the image to make more room down there.
3) I felt her face had a little bit too much meat on her left side but if you're going for something more distorted then don't worry about this.
4) I flipped the other character, I felt like I wanted to see what she was facing and now it also goes with the flow of the curve.
Lastly if you want more depth to your work try using a few more values. Hope thats useful and good luck.
Here's my work http://guang2222.deviantart.com/