Lots of ways as LQ says Blitzer.
I have a stock of the old Humbrol 'Track Colour' that was used for railway kits. It is a great old rusty colour but sadly no longer available. Anyway, I base coat the tracks this colour. Then I apply a few washes using Burnt Umber oil paint thinned with White Spirit. Then I mix a little Burnt Sienna with the umber to make a dark reddy brown wash.
I dry brush the steel parts a gun metal colour and then the parts that get a lot of wear get dry brushed again with the same colour but with a little silver added each time - don't make it too bright though.
After this I give it a light overspray, usually of Tamiya Buff lightened or darkened depending on the ground work I have chosen, to represent dirt and dust. If you are going to do a muddy version, then you need to paint the added mud and dirt after the basic work to the tracks has been done.
Then I use pastel chalks to blend the vehicle ground work, any figures and buildings, etc, together.