First things first then. I don't want you to think that what I'm about to say or show you is the only way to do things. Mainly, all I'm about to show is to loosen up your art a little. Also, realise I didn't spend a whole lot of time with my additions, so please don't think that this is how your final piece should look.

Now, on to the critique. This piece looks unfinished to me. You have some great tones layed down, but now you need to clean them up a little. I won't go into detail about the facial structure looking a little loopsided, but I think you need to look at her eye placement just a bit. They are either to far apart or not big enough. But that's a small issue because she might actually look like that.

Now on to the actual things I can help you with. First things first. You need more contrast on the face. I don't know if you are trying to do a dry brush look, which is fine, but I think you need to keep you piece's consistent throughout. The fingers are blended together well, and you have a good sense of contrast there. So that's why I circled them in the blue. Now the cheeks, and chin could use more highlights. Which I show you here:



The next thing is the hair. Great value so far, and lends nicely as a base to work from. One thing to note about hair is that it flows, like water, and has a sense of volume, ie, highlights, mid tones, and shadow. One thing you are missing, besides the flow, is mid tones and strong highlights. This is actually pretty easy to do.

1. Create your shapes and form of your hair in one layer. (For example, I used your hair that you have so far as this layer)
2. Make another layer, just on top of it. Select the brush tool, and set it to change size and opacity according to the stylus pressure. Also select the brightest highlight of your hair.
3. Begin drawing your hair, and be sure to follow the forms you've already layed out, and you can make a stray hair or two for added effect.
4. Once you are satisfied with how you have layed out your hair, it will look stringy, believe me. But now, duplicate that layer. On the duplicate hair layer, go to guassion blur and soften the hair a bit. With the other hair layer underneath, you will see that it gets an amazing amount of form from so easy a task.
5. Next, lock the transparency of the layer, and select a large fuzzy brush. Pick a medium color, and set the brush to multiply. In the unblurred hair layer, begin lightly brushing the shadows of the hair to make it a little darker.

Next I would suggest softer highlights on the clothes. I don't know what your reference looks like, but your highlights just look to strong.



Overall though I like what you have so far. But like I said earlier, it just looks unfinished. I hope this helps a little.