Once you are confident with drawing a basic oval shape that is roughly 1 to 1.5 in proportions, start practising adding in the features. Compare the oval canon (method) to the circle one below)

Don’t worry about perfect lines, no shading or details at this stage. Just get some practice at sketching the average proportions of a male and female adult and the differences between adults and children. Of course, everybody is different, but when observing faces, it is great to have a standard (or canon) in mind to then pick out the variations with your subject.

See the divisions overlaid on Tom Cruise's face here

Compare the circle method, where you start with a circle (a sphere) with the sides chopped off, so it looks sort of like a fat cheese wheel (the side on view of these new inner circles would be 2/3 the diameter of the main circle). Then the hairline is about at the level of the top of the smaller circle, the brow at the middle of it and this establishes the distance from brow to nose tip and nose tip to chin. (3 equal divisions).

Here is a rough sketch of this concept front on:

*The circle is sliced down to a cheese wheel shape at the sides.

* The 3.5 lengthwise landmarks are the chin to base of nose, base of nose to eyebrows, eyebrows to hairline (0.5 to top of head).