This tutorial is a step-by-step guide showing my own style of shading a face.
I usually use the fill tool and just draw a big circle for the head. The color is the base skin color, so basically light brown. By using the fill tool, i can shape that circle into a head figure of a human. Which actually really easy, use the white color to erase the unnecessary parts. Then, i use the fill tool again, this time with darker tone.. this is for the shading of the eyes...
Manga shading - Again with the same darker tone, both sides of the head (refer picture). As u can see, this type of shading style is really an anime style of shading. Anime/manga style shading usually not using more than 3 color tones, which are the base skin color, darker, and lighter. the style is so simple, the colors are not blend in with each other and the different between is very clear.
By using the Airbrush tool , u can blend 2 colors. Use the darker or lighter tone, and select 50% of transparency. Change the pen thickness to 3/4 and use it between both colors. try with lower transparency (10-15%) to make sure the color really blend in together. This way u can get a realistic style of shading.
This shading style is really easy as long as u know where to shade correctly. U have to get the 3D look on the face, refer next image
Shade it like this
This is one of manga style eyes.. i drew this by using the Pen tool , 3 on pen thickness, 30% on transparency. If u refer to image5a, its easier to make it balance by drawing to lines on the eyes part which I highlighted with red.
u have to make it balance
This is the final result for the eyes, i always like to draw Tetsuya Nemura style of eyes.. i'm not sure how he did it, but i think the eyes i drew look okay too.
Again, u can re-shape the face however u want after u done with the shading. Use the Fill tool again, select white and erase the unwanted part. In my case i wanna draw an adult men, so i decided on a longer and thinner face, as oppose to kid face which is chubbier and shorter.
Use the darker tone again and draw the shading for both mouth and nose. U can start with the manga style shading first and use airbrush to blend in the colors again.
Basically, the lighter tone only used at some parts such as the nose, cheek, lips, and forehead (refer image9a) u can directly apply to it with airbrush tool, lighter color, 3-4 pen thickness, with 10% transparency.
here the result with lighter shading in place
Add hair or facial hair and finish the drawing already.