First decide where the tank will be in service. That is if its on parade the tracks will show worn steel with the rubber pads looking more or less clean. For this look spray the tracks silver, use a dark brown / black wash and dry brush the rubber pads a black w/ a hint of sky blue.
Best to look at reference photographs of tracked vehicles in service
similar to the one you are building. Use photographs of other modelers
work for ideas yet strive for realism, some get carried away with
bright orange rust and forget to show worn metal on the wear points.
Now if this vehicle is serving in Vietnam spray the tracks the typical 'red mud' color and drybrush the worn steel & pads the same way.
Basically the dirt will collect in the crevices, the pads and steel wear points will need to be painted (dry brushed) last.
The dirt can be added as a wash towards the finish, as it will give the same look as stated above.
Another way is to finish the tracks in the mud / dirt colors and use a lead pencil to hit the wear & contact points. This looks realistic yet many end up missing the contact points inside the guide horns & wheel surfaces. This technique is easier to do before installing the tracks, just dry fit them first to avoid frustration later on.
Of course actual metal tracks are the ultimate in realism, they sag like the real tracks and weathering consists of sanding the paint (mud / dirt) off to the metal, just like real tracks!
Which technique is the best? The one with the results you strive for. Just go for it & if you are not happy set the scene in mud or use the experience to better your next project.