Welcome to my tutorial on shading.


First we will start with the basics. Select what size of head you want to make (for this i will be using a 512x512).


Then go to "Image>Guides>New Guides (by Precent)... Make it vertical, and posistion (in %):
50.


It should look like this.


Next make a new layer, and select the paths tool. Make a simple design.


Then Alpha select the layer with the design on it like so.

Then select the Air Brush and make the settings look like the ones in the image below.


Now lets start shading, with the image alpha selected, your brush won't go out side the lines, so it will look nice and neat. Start by taking black, or a Darker blue and shading the underneath part. (note: make the brush bigger if needed)


Next take a lighter blue or just plane white, and start highlighting the over area.


Ok, thats the basic, and easy way to shade with high quality results. I hope this helped.
(finished head)