Semienigma
http://www.howtodrawmanga.com/howtodraw/tutorials.html#ex_books_start here.
Nuuuuuuuuu. Not the howtomanga! Stay away from those books!
Anatomy books are the way to go if you want to get better at drawing whatever. I'm trying to animate a 3/4 from behind model walk right now and aside from looking at a whole whack of youtube videos and prodding friends for tips for walking in high heels (I hates them!) the most helpful thing I've had is my anatomy books and looking back, checking to see how the back will rotate in space, how the shoulder blades are going to twist and all those subtle little things that you'll be able to see even in a cartoon stylization.
I'm also modeling a girl in 3D, again, direct reference is my best friend in this and pulling out from what I know about anatomy. For example, consider this: when girls are asked to do a self brest exam for cancer we start or end in the armpit. That's because the breast ends there, it's not just a ball stuck onto our pecs, they wrap around us a little bit.
Ninota posted this anatomy book a while ago and after flipping through it it's pretty high quality stuff. Use it. There's a good section on the neck that should help with looking up and down and around.
http://www.archive.org/stream/cu31924014504371#page/n13/mode/2up
And finally look at yourself in the mirror. watch your nose how it turns in space, check to see how you skin/muscles stretch when you look up and think about what your chin would look like on paper if it were a box based on how much you can see below it. Look in the mirror again, ask yourself if your face is a constant round thing or if it has any other sort of dementionality to it. Look at life, then ask questions.
