Instructions:
Zooming out, you'll see that the hair looks really nice already. If you don't care to do that much more, you can stop here.

What I generally do at this point, though, is to fix the hairstyle. I've usually painted using the first clumsy blocked in shape and now that I can see the flow of the hair better, I'll go in and just fix the edges up. I'll push it in in one place and out in another, perhaps, so that the shape of it follows the locks I've painted. Using the trick of painting individual strands of hair on a separate layer and very lightly blurring or smudging them, follow the outline of the hair and add some 'frizz' to it. It still looks smooth and sleek but there's more life to it, now.