Exercise 3.1. Draw a simple cartoon character with the Paintbrush tool. Use a tablet if you have one. Draw clean, solid lines.
Exercise 3.2. Colorize your drawing (or find some clean line art if you skipped the first exercise). Refer to 3.1 Tutorial: Colorizing a Drawing for tips on where to place your line art layer and what mode it should be in. Add areas of solid color to your character.
Exercise 3.3. Now try using the Dodge/Burn tool to add shading to one part of your character, and then use the Airbrush tool for a different part. Use whichever method you prefer to shade the rest of the cartoon character.
Exercise 3.4. Use the Smudge tool to blend the shading. If your character has hair or fur, use the Smudge tool to add it.