Start off drawing the outline. I like to do an M shape on the forehead so the hair doesn't look too limp. Just do some little lines for the end, that'll be sorted out as we go along, it's not too important at the beginning.
Using 2 start putting in some strands. This also gives direction to the hair which is useful if it's wavy or curly, but as this is straight there's not a lot to them. Some little flicks at the end stop it looking to poker-straight. Also shade where it tucks behind the ear and behind the head and neck.
Now fill in the rest with 4 and change the outline to 1. You can actually do that whenever you want to (heck, you can start with 1 if you want, I just use black because it's clearer), but it made sense to do it now.
Using 3 build up the shading from step 2. This is mostly extending the lines you already have. Colour over the strands in 2 if they look too long and dark. You don't have to outline every bit of colour 2, I find the contrast of 2 next to 4 (or even 5) makes it look more like strands of hair then one big blob on her head.
Now start with the highlights. I really can't explain it any clearer than just showing it, put them in the big unshaded areas and don't worry too much if you have 5 next to 2 or 3. A few H shapes makes the hair look shinier, so add a few diagonal H's at the top of the hair and maybe a couple further down too.
Add to these highlights using 6. I've only put them on the top of the head, on a base this size too many highlights further down makes the hair look wavy which this isn't. If you zoom out and think there are too many or too few highlights anywhere just add more, it really depends on the colour of the hair and the size of the base.
Using the lightest colour of the hair and the darkest colours of the base shade under the hair where it casts a shadow on the forehead.
