Oh man, I LOVE drawing hair. It's my favourite thing to do(odle) so I'll share what I can.
I've found that when it comes to drawing hair you need to make some major commitments right off the bat. Commitments like 'this person's hair is straight' or 'this person's hair is long and full of braids' etc. Presuming you've already made these decisions (and they can always be changed) I'd say much of what makes good hair in a drawing comes down to lines and shapes.
If your character's hair is straight, consider the weight of the hair and where that makes it fall. Thick, long hair is pulled flat at the roots (close to the skull) because the rest of the hair is so heavy. You get drapey shoulder curtains with hair like this, and a Jessica Rabbit style.
Thin straight hair on the other hand might be a bit more lofty and tufty (if short) or flat and limp (if long).
Curly hair is more complex. It can be thick or thin, long or short, coarse or smooth, and these things affect where the body of the hair (and therefore it's shape) will fall. Thin, short, curly hair may be flat at the roots and curly on the ends around the ears and jaw-- think typical teenage boy hair cut. Thick curly hair is bigger and more unruly, deep at the roots around the skull and then out in all directions (short afro) or a kind of broad triangle (long).
Thick curly long:
More curly:
There are so many variations are mixtures of hair styles that I can't possibly describe all their features, but the texture and thickness of hair will give it it's shape.
Once I know the shape/look I need, I find lines are the next important thing.
Silky clean hair will have fewer lines in it than dirty hair. Imagine greasy 'rat tail' hair vs those luscious curls you get from Herbal Essences-- one is like spaghetti, one is like ribbon.
Dirty hair:
Clean hair:
In that picture I did of the ghost kiss, I didn't need many lines for the ghost's hair. It's silky and weightless, ethereal, so the ends would need defining a lot more than the mid-length and roots (which aren't moving much). The gent she's with, on the other hand, has tufty curly hair, so actually drawing his required a lot more definition.
Here's some more points on hair I did for West Extras:
And here's some examples of hair I've described here.
Curly short (monk)
Straight and kind of electrified, I guess? But you can see how the addition of lines describes a style.
Sorry, little bit NSFW: But you can see tufty short, thick wavy long and short thick straight .
ALSO consider swapping hair for a head dress or cover. Variety is the spice of life!
That's all I have for now, will add more if I can think of anything important.
