Did a partial edit. Man, I am out of practice. Head, neck (too much neck maybe), one shoulder, upper torso. Gave her some pants, I mean come on. Cheesecake or not, that's just an awful costume. I included some intermediate copies of the face. Helm's edit did a better job on the arms and legs than I would have anyway.
I think you need to work on anatomy study and expressing form (3d-ness). Also, too many colors in the original, I think. You could get away with (skin, blue, extra saturated stuff like lips, extra desaturated stuff for silver and background), 5 colors each for about 20 colors total. But other people here are better at colors than I am.
Steps on the face I used:
- Given the size of the head, determine the size of the eye (eye width is approximately head height divided by 6 or 7).
- Sketch out a couple of eye shapes, and pick one.
- Put the eyes in the head.
- Sketch the other reference points: base of the nose, mouth, chin, hairline. Add a preliminary cheek and jaw line. Move the eyebrows around as needed.
- Fill in lights and shadows. This is to add in the shape of the underlying skull. So the eyes get sockets, the nose gets lighter, as do the cheeks, chin and forehead. I didn't shade in the eyeballs or lips yet, just the shapes of the head. I think I added a bit of AA to the jawline. Oh, I added a lot to the top of the skull too - she had a very flat head. No reference used.
- Then go back and color in the actual eyeball, and lips. This got me to the third face on the right. I confess I think I like this one the best, but at the time I wanted to tweak it some.
- The last head on the right is the same face but made thinner by one pixel. Then I tried a rounder jaw, which is what is in the full sized version.
Clarity is very important. The eye shapes I used are not much different from the eye shapes you used, but I kept the shading simple. But mostly it is the lack of form, and wonky anatomy that is hindering you.
Hope this helps,
Tourist