TRSE: How To Draw Tutorials:
Basic Positioning of the Head

    Recall those vertical and horizontal outlines I suggested that you draw to keep the face leveled? The horizontal is always perpendicular to the veritical line no matter how many different angles of view the head is drawn in. If you stick a ruler to your face, it won't change its position as you move your head around (those with glasses may know what I mean).
   I mentioned before that the horizontal lines can be adjusted to get different porportions of the face (like longer face or shorter face) and that same method can be used to give the head a 3D look especially when the character is looking downward or upward. Look at the diagram (made few minor misshaps so please excuse them) below for examples.

    Note how horizontal lines narrow when a head is moving downward and once the head have fully turned downward, the chin would be almost reaching that nick at the top of the chestbone with the nose almost touching the mouth. That is something many novice artists (and even some manga artists) forgot about. The hair bangs also start to cover the upper parts of the eyes as the head is moved downward while the center of the head shifts toward you.  The hair behind the hair might raise a bit as result of being "lifted" by the movement of the head. When the head moves upward, the eyes shrink before disappearing from the plain view. Let's take a look at what the side views of the heads are like when they reached their highest and lowest limits.
    When the head moves upward, the neck gets bit stretched and the "Adam's Apple" tend to become more obvious in most people but that's optional for any artists. The neck also moves forward when the head is turned downward sort like a level. In some cases especially chubby people, the neck tend to develop wrinkles as a result of compression of the skin between the jaws and the neck, but don't worry about that until you're experience enough to take on such "small details".

    Let's show how the head moves from a side to a side. The diagram below represents five most common head positions in Animangas.

    When a head moves to the side, the cheek on the further side and the eyes get thinner, and since the nose is furtherest point of the face, the nose "shifts to catch up" with the eye on the further side before hiding that eye completely in the side view and it's true for the mouth too. Because of the fact that the face is not flat, the vertical line should be used only as a guide, otherwise, the face would look too flat. The nose has to be away from the vertical line so to give the face more rounded/3D look. The chin also tend to become more obvious as the head moves to the side but that's for advanced artists so don't worry about that for now. There is a limit to how far to the side the head can move.
    If I remember correctly, the head can move only within a range of 120 degrees, (60 degrees to either side) NEVER 180(90 to either side) degrees or beyond!!!. Having the head positioned at 90 degrees from the front is a common mistake made by many artists out there. In order for the characters to take a look at what's behind them, they always have to twist their entire bodies in order to look past their shoulders and even the legs had to shift a bit too as I found out. Don't forget that "little detail"!
    As I said before, no matter where the head is shifted to, the imaginary horizontal and vertical lines always stay perpenticular (+) to each other regardless of how rouned/flat a face is. The horizontal lines themselves can be narrowened and widened to give them some basic 3D look when looking upward or downward and one side of the face always shrink before disappearing from the view as the head move to one side. That's it for the positioning of the head. Owww, my poor neck....