How do I make a meshes in a game look cartoony?

How is this done if possible?

Bake the material using a toon shader

Model it with simplistic, organic shapes, and use mostly simple solid colors for the textures. Basically, avoid roughness and grit. Cut polys from where details would be on a more realistic mesh, and use them in joints to make them bends smoother.

If you’re just asking about the shading, I recommend using GLSL and playing with the toon shader at the materials window ->shaders tab ->top pulldown (it defaults to Lambert) adjust the smooth and size values to your liking.
Alternately, many toony games don’t use shading at all, just make sure that objects and scenery are distinguishable from each other.

And don’t care about proportions, bigger heads and hands looks cartoonish too