Face concepts

Here I am quickly sketching up some face concepts, which will help determine the appearance of my character

With this one I was trying to draw different face shapes / structure 

When drawing a face it is important to learn how to draw the skull or at least where everything goes as it will easily help you set guidelines of where the facial features are

This is an image I found  and below you can see this artist use's this to establish where to put the features 

Once you have mastered this then designing proportional right characters will become easy

 

Here is another example I have found which demonstrates the extent you can got to in drawing a face