This is the walkthrough for this:
For my full painting tutorial, please see here:

1. Sketch.
Straightforward enough. I had glasses in the sketch but I erased them because I didn't end up painting them. I didn't include details like eyelashes in the sketch.

2. Colour Blocking.
Vague splashing on of sort of skin tones and hoping for the best.

3. Blending
It looks like a big leap but it's really not. Just take a big, soft brush on a low opacity and keep one finger on alt all the time XD Work quickly to blend and it comes together really nicely.

4. Some Detail Definition
Starting to form where the eyes will be. I took a hard brush in a dark colour and defined the nose and the mouth a little more.

5. Eyes and Lips
Eyes take ages but they're really fun and you can basically do whatever the hell you want with them and they'll come out nice XD It doesn't matter if you do eyes "wrong" it'll look like a style thing. Lips are hard. I kind of make it up as I go with lips.

6. Basic Hair
I used three colours in varying brush sizes and opacities to form the basic shapes of the hair. I worked on about five layer for this. A section for her fringe, and one for the bangs in front of her ears, one for over her shoulder, one for the back and one for the back back (for depth's sake).

7. Detailing Hair Part 1
I did two things here. One was take some smaller brushes in lighter colours and do loads of little strands for detail and to make it look a bit more realistic. The other was to take a large, soft brush and a medium hard one in a dark colour and start to block in some shadows to stop the hair looking flat, like it's on one layer.

8. Detailing Hair Part 2
Teeny tiny brush in a near-white colour at a high opacity, and a shitload of strands. Also I did the highlights.

9. Finishing Hair
Doesn't look like I did much here. I gave the back layer a 5px Gaussian blur and the back back layer an 8px Gaussian blur. Then I got the history brush (save regularly and reopen so you can incorporate the history brush into your painting!) on a hard seting but low opacity and slightly erased some of the blurring. This is so that the focus is shifted so rather than the whole picture is in clear focus, you're directed straight to her face. It's a silly little trick but I love it.

10. Shading the Face (Again)
I took a dark colour and added some more shadows onto the face. This includes the ones cast but the hair and deepening some of the others to add detail like around the eyes and nose.

11. Highlights
I picked really yellowy ones because I usually go for blue and she's surrounded by golden hair in golden light and it just seemed nice. A few highlights around the corners of the eyes and on the nose make all the difference in the world.

12. Feature Detailing
Added fweckles (bad ones), highlights in the eyes and did some colour adjustments on the cheeks and nose to make them pinker and cuter and whatnot.

13. Finishing.
Various overlay layers and level adjustments and blurs and opacities and whatnot to make it all shiny and golden and pretty.

Now I need to sleep. It's 2.15AM.