Step1:

    Draw two circles and overlap them like in sample 1.   Then draw in some lines like in sample 2.  These lines will be used as a guide when adding the features..

    skull1

    Step 2:

    Once you’ve mapped out where the features will go you can start to add detail like in sample 4.

    skull2

    Step 3:

    Now erase the guide and shade in your skull.

    skull3

    Step 4:

    skull4

    End Result