A while ago I had the rare chance to talk to Urbanator (Deviantart, Patreon, SFMLab) about post-processing. If you don't know him, he's an SFM artist that brings everything to the next level because of his attention to detail and a delicate, gorgeous smoothness in his work.
I didn't have the chance to put anything into practice until very recently because of exams, so here's a tiny test.
The main idea of the exercise is to remove out of place pixels and horrendously jagged edges (which SFM is famous for), as well as soften lighting and texture.