This section is from the book "Complete Self-Instructing Library Of Practical Photography", by J. B. Schriever. Also available from Amazon: Complete Self-Instructing Library Of Practical Photography.
Pose Of The Head. Although it is not necessary to pose subjects whose features are normal, it is, however, essential that strict attention be paid to the various features of the face, turning the head to give the most pleasing appearance and to avoid any exaggeration of lines. For instance, with a subject having a nose that turns up, do not raise the chin too high, but rather have it slightly lowered. This will give length to the nose and tend to lighten the curve. If the nose is a drooping one, raising the chin a trifle will have the effect of shortening its appearance. For the average subject, the chin should be held just a trifle above the level, providing the camera is placed at the proper height. The raising or lowering of the chin must be done naturally. Be very careful that the subject docs not extend the chin forward or draw it in. It is best to request the subject to make any change of position which you may require, rather than to place them in the required position yourself, because under your handling the subject apt to get a feeling of stiffness, which is bound to appear in the finished picture.
The Mouth. Of all the features the mouth, perhaps, gives the most expression to the face, and it is, therefore, necessary to pay special attention to this feature. Should the mouth be closed tightly, or if it be slightly opened, do not ask the subject to close or open the mouth, for by calling attention to it, there will be danger of their going to the extreme. Usually, conversing with the subject and asking them a question which will bring a pleasing answer, will result in the mouth being properly closed, and it will then naturally shape itself. It is permissible, at times, to request the subject to wet the lips, which will produce a slight gloss on them, and at the same time a more natural shape will be given to the mouth. In the case of chapped lips, they can be greatly improved in appearance by this slight moistening.
The Eye. It is seldom that a subject looks well with the eyes cast downward. The direction of the eye should be slightly upward, turned so as to lead the face; i.e., if the face is directed to the right the eye must lead to the right. By having the eyes turned slightly upward-a trifle above the level-you produce more roundness and better expression than if the subject were looking on a level or below the level. The latter tends to give a sleepy appearance. Do not go to the extreme, however, as the white of the eye should never show below the pupil.
Catch-Lights In The Eye. The surface of the eye is a reflecting medium, acting like a mirror and reflecting the light coming from the skylight. The location of the spot of reflected light on the eye is governed entirely by the angle at which the light falls upon the subject, and the position of the face toward or from the light. This spot is termed a catch-light, and its size depends upon the distance the face is from the light; also upon the size of the source of light. If the lighting has been made correctly, the catch-light should appear on the upper corner on the light side of the iris of each eye. On close examination, an exact reproduction of the skylight, or source of light, in a miniature form, will be found to appear in this catch-light. It should not extend into the white of the eye, nor should it touch the center of the pupil.