Jh's Sketchbook! Study. Practice! APPLY!

[MrFrenik]

To avoid the "plastic" look in your faces (and all rendered objects) try to use less value range to turn your forms, and focus mainly on using middle/darker values as most saturated colors lie within the middle of the value scale and down. I'd also suggest getting away from the soft brush while you're getting used to rendering forms and try to focus on confident brush work as well as painting the larger planes that make up the masses. Starting out with painting the basic geo-forms (cube, cylinder, sphere, cone) is great practice and I highly recommend it, despite how boring it might seem.