Drawing the Angled Head

It's quite common when figure drawing that your subject's head will be at an odd angle. Not too often is your subject looking straight at you. The proportions and perspective that you see when the face is looking straight at you get blown out of the water when the head moves to an angled position. You won't be able to rely on standard proportions so you'll have to for sure draw what you see, and not what your logical mind tells you what is there. There are, however, some things that you can keep in mind when drawing an angled head to make it easier on you.
When the head is looking Downward:
You'll see more forehead and top of the head than chin or bottom of the face.
The ears appear to be higher up on the head than they actually are.
You can draw an imaginary vertical line that bisects the face. As the face turns, that line will turn with the face and become a sharper arc as the head turns.
The nose appears to be longer and lower on the face than it actually is.
Since the face is not a flat plane, but a curved surface, you can draw an imaginary horizontal line through the eyes and mouth. The more the head turns down, the more the imaginary horizontal line arcs upward.

When the head is looking Upward:
You'll see more chin, neck, and bottom of the chin than brow or forehead.
The ears appear to be lower on the head than they actually are.
You can draw an imaginary vertical line that bisects the face. As the face turns, that line will turn with the face and become a sharper arc as the head turns.
The nose appears to be shorter and higher on the face than it actually is. The nose can be see as a triangular shape.
Since the face is not a flat plane, but a curved surface, you can draw an imaginary horizontal line through the eyes and mouth. The more the head turns up, the more the imaginary horizontal line arcs downward. These imaginary horizontal lines will help you to place the eyes and mouth.

Each image below is clickable so you can get a better look at it. I drew the head in blue, and drew the construction line bisecting the face and the lines across the eyes and mouth in pencil.
 

When you draw an angled head watch very closely what you are doing and measure your subject often. Because "normal" proportion gets thrown out the window, you'll have to rely on measuring one element against another element in order to create the angled head correctly. When the subject has a lot of hair, it makes the drawing that much harder because you can't see the scalp, and so you'll have to guess where the scalp is under all that hair. Finding the scalp will aid you a lot in finding correct proportions to the head.

To draw an angled head, draw an oval as close to your subject's head shape as you can, then bisect the oval vertically. Then draw the two arced lines representing the eyes and nose. Measure what you've drawn, and if anything is off, erase and draw again the part that is incorrect. Then draw in the features on the face. If you need some instruction on drawing the features of the face, check out the Drawing Portraits tutorials.