I painted my first tank for my Soviets. Initially I hadn't varnished and smoked the tracks so the mud looked completely dry. I'm happy with the result now.
Unfortunately the scale is different from the one my regulars use so I guess this is mostly to put in the cabinets or scenarios in which it is the only piece of armour present.
Needless to say it was a quick job. Green undercoat, Vallejo seipa wash, drybrush with off white and then rust and mud on the tracks.
Rust was simple M*I*G* powder in water applied in generous amounts all over the tracks. Didn't really look convincing... a lot less should probably be used.
The mud was made from wall paint, sand and filler. I kept on adding filler til I got a fairly high viscosity that could still be delivered by brush. Once dry I painted the areas that were going to be wet with Vallejo Smoke and then gave them a thick coat of Model Master Semi-Gloss varnish.