Here's some of my work. The first is a simple wash using cheap craft paints thinned with water then fixed in place with Krylon Matte Finish. As with all my cars, the wheelsets are painted with alternating daubs of Testor's Rubber, Flat Brown and Rust.
The second one is done with Scale Rail Graphics decals and daubs of paint pulled into streaks with dirty thinner as a wash. Then when dry, I dusted it with powdered pastels then fixed them in place with Krylon.
The gon doesn't show it well in the picture but it has bulging in its panels, done by applying a hot soldering iron close to the panel, not enough to touch but enough to soften it then push it out with a fingertip. Daubs of paint were then streaked with a dirty thinner wash. When dry it was coated with the Krylon Matte.