Tutorial - Posing a model.
The head and the face.

Very few faces can withstand being photographed from the front. Most have asymmetries that go unnoticed in real life or in a three-quarter but which stand out in a full-face photograph. Many people, for example, have one eyebrow higher than the other. Sometimes it's an eye that's bigger or at least more open. The nose or chin are not always well aligned, and so on. For this reason, faces are often photographed in a three-quarter view, which also makes it possible to conceal a scar by orienting the face on the most flattering side.

But when you're lucky enough to come across a perfectly symmetrical face, don't hesitate to try a frontal shot. It's really quite beautiful. But play up the symmetry all the way: use front lighting so that both sides of the face are lit in the same way. See also portrait lighting tutorial.

Note that good professional make-up is perfectly capable of correcting slight facial asymmetries..

Three faces that can take a full frontal shot