Hi, Phil!
Wow, lots of techniques here!
For the tracks, I would suggest a rusty brown colour. As the tracks wear the natural metal of the track will come through and look like real tracks.
Dry brushing is a technique that is exactly as it sounds. First the model is painted and allowed to dry. To dry brush, lighten the paint you used slightly. Dip the brush in the paint and wipe just about every bit of the paint off and rub it on a paper towel. What you want is a brush that has virtually no paint on it. Lightly work the brush across the edges of the model and on the raised details like bolts etc. The high points will pick up traces of the paint and give a slight contrast to the rest of the model.
A wash involves using a brush and a shading colour that compliments the base colour. The shade colour is thinned to be very thin and it is allowed to flow into the nooks and crannys of the model. This gives it a bit of depth. There are many paints to use but it's best if you use one that is compatible for your base paint. If oil based, you can use a water based acrylic paint. The water won't affect the base paint. I've used ink and alcohol to wash some models with, other times paint and thinner. You want it really thin so when the solvent evaporates verty little remains of the wash. If you want it darker, let dry and repeat again.
The best thing though is practice. If you have a scrap model, practice on that.
Some modellers keep a log book for paint mixes, wash ratios etc used on each model. If one likes the finish, it can be used on another by just referring to the log.
Good luck and don't be afraid to ask questions.