An excellent followup to Modeling Basics is Texturing.  This series explores the various approaches to material creation with an emphasis on painters' needs.  For illustrators, Textures don't always need to be extremely high-quality and time consuming.  They're often created with the 2D paintover in mind: only a base coat on which to add details in the illustration phase.  The series also introduces the texture preparation step called 'UV unwrapping', a notoriously confusing concept which vexed me for years.  Though I'll be demonstrating with Modo 3d and Octane Render, the principles apply to most modern 3D packages (including the free blender 3D).