Start with two different sized circles like below.  Sample 1 will be our guide for a full face view and sample 2 a side view profile.

    Step 2:

    We need to now mark out where the features will go.  Study the samples below and see how the linear guide will help.

    Step 3:

    You can see how the linear guide helps us to draw in the features.

    Step 4:

    We can now add the cheeks, jaw, ears and hair.