Just finished doing a tiger head construction demo for a student. Figured you guys might benefit from it as well.
One of the most important things about head construction - and this goes for human heads as well - is seeing the various parts of the face like pieces of a three dimensional puzzle that wedge together. Related to that, is understanding that the face is made up of many planes, meaning that there are many edges where these planes meet.
When we look at a face, it's easy not to notice all of these planes and puzzle pieces, because it all looks smooth and polished - but they're there, and they're the key to constructing a face that looks believable and that catches the light in a realistic fashion.