For hair, I'd like to suggest not doing highlights like that, instead, do it more zig-zag and don't do it around the whole thing. Also try to shade more solidly, soft doesn't necessarily equate to good.
Now gonna move on to her arm, the hands need more work and detail, hands have shading, too~ And I find it quite odd to see both arms having the same shading, because when your hand is up and the light is shining on it, there shouldn't be as much shading, instead, put some light shading to the right of her raised arm instead. And from the picture, I see that you color collarbones quite oddly try putting a highlight shade on the collarbone itself, and then some shading slightly under, around the width of a finger.(her finger, of course~)
Her arm starts out too small, to make it easier, If you sketched a circle for the head, try drawing 4 circles to fit nicely inside, then with that size in mind, put it on the shoulders. Her waist is too small, as well. Also, don't shade everything as a different object, remember, there is one or more light source, that shines on everything, not just one object. The blue part of the skirt looks very "pillow shaded" and the white have been ignored.
End of long critique o/