Okay, we start off with the hairline and go from there. I've done a fairly non-committal flop on one side and tucked the other side behind her hidden ear, partly because I usually have my hair like that and partly because in a space of so few pixels I find I tend to shade both sides in the same way if I make them do the same thing, and that's kind of boring.
And now for the outline. I just do a few big waves on the outside which are fairly straightforward. It's really up to you how loose you want the waves to be. On the bits that fall down her front I tried to make the waves smaller as I got to the end of her hair because there's less weight holding that hair down so it's springier. If you make these bits thinner towards the bottom it makes the hair look vaguely layered (or at least not to big and fluffy). Adding loose strands makes the hair look more natural as well as more interesting. Again, it's up to you how messy you want your doll's hair to look.
Oookay, now to start shading. I can't really explain this very well, but I pretty much just put in little H and h shapes, with the odd y thrown in wherever they fit. I generally but them in areas where the outline curves in, but if you're using a big base you might find you have room for some in the middle of areas where the outline curves out too, and that'll mean the hair doesn't look as much like it's waving in unison. Also add some shading at the parting and where the hair tucked behind her ear is covered.
Here I just filled in with a colour two shades lighter than the first shading colour, and changed the colour of the outline. I only used blue to start with because I find it easier to see what I'm doing when I use a colour that's nothing like any of the base colours (and the hairline, so I know which bits to erase when I'm done with it).
Build up the shading and start making wavy sort of shapes leading off the Hs, hs and ys. You can see that I've gone over some of the original shading with a lighter colour because I don't want the shading to look too severe. It's best to keep zooming out so you can see if you're making smooth shapes. It's a bit hit and miss, this shading, so you might find you need to tweak bits as you go along.
And now we start adding highlights. Just fill in the blanks between the shading. You should find the shading has pointed out obvious bits that look like they need highlights. I know that's not especially helpful as a commentary goes, but that's really all there is to it.
Add some lighter highlights where there's space for them.
And now shade the outline. It's your choice whether you do this bit or not, but I find it looks much nicer, especially where there are highlights right up against the outline. I made the loose strands get gradually lighter, but not so light that they'll look silly against a darker background. I also made the bits pulled back from her forehead lighter so they'll be easier to blend at the next step...
...in which I add shading on her skin and clothes. I found a colour between one of the middley ones from the hair palette and one of the dark ones from the skin palette because I found I needed it. It varies depending on the difference between these two palettes as to whether you'll need to do that.
