This is what I usually do
1. Start with a dark brown as a base coat first and allow to dry a couple of days ( 1 should be enough for acrylics but I only use enamels on rubber band tracks to give it bite)
2. Next go with a very dark (almost black ) wash and aloow to dry 1 or 2 days again.
3. Drybrush starting with the original color and progressively lightening it until it is where you want it, sometimes I go almost to a bright rusty orange but that is only for high humidity dio's such as SE asia, you dont want that much for the desert.
4. Again allow to dry a day or two. Then I usually start with Testers steel and initially do a heavy dry brushing on both sides and allow it to dry. Then I use various metallic shades that are brighter than the steel and usually go to Titanium or Aluminum for a final drybrushing usually only on the cleats and guide teeth these seeing the heaviest wear.
Some people even use pencil graphite as the final color. Hope this helps.