I am slowly learning little weathering techniques, but am cautious about weathering, as I would hate to screw up something I worked on so hard. I like light weathering, myself. Trucks get dirty whether we like it or not, especially if you go to the places I go, but I do like a model that looks like a truck that's driven. I wash mine as often as I can, though.
Here's an exhaust manifold I did. The flex pipe is shiny because they eventually get replaced, often by themselves.
Another weathering trick I did, mis-matched(by brand/tread pattern/age) and worn tires
I did it to the tractor as well. You'll notice I made the forward drive axle tires look worn and the rear drive axle tires pretty much look brand new. It's common to see this on real trucks, especially in fleets.
As time goes on, I will get more into the weathering.