learn what skeletons look like; after all, under the skin and the hair and tissue, we're all just skeletons on the inside.
this may seem like an odd step, but since skeletons are the bones of how we look, they also need to be the bones of how we draw too! making sure that there is enough space for the eye sockets and jaw and nasal cavity (nose hole) will ensure that your drawing looks realistic to the eye.
you won't need to do this step every time you draw a face, but when you are learning to draw it it can be useful to use it as a reference.