Just few simple starting suggestions to enter the face arena and get some built-up skill very fast:
1) look for classical proportions You should start from on some tutorial (and the relevant differences between men, women and kids)
2) make copy excercises (from pictures, drawings, comics ... what You find easier to spot and reproduce the parts and features)
3) look for shapes better fitting the face (not a ball or a mere ellipse), eyes (not a symmetric oval) nose (not a mere triangular prism), mouth (not another oval or rising moon) etc. You may do better choices after copying many faces and get familiar with drawing them and their relevant curves.
Try to see the head as made of the cranium (above), an eyemask, a nose protuberance, cheeks and their relative bones, the lower jaw with the chin. between the chin and the nose You eventually see the lips.
The neck and the hair would be also important to study to complete a face in a satisfactory way.
Panta rei (everything flows)!