Well, if you are glassing it, then I'd study the detail and add more material to raise the textures. Or you could bondo the glass and detail it that way. If you arent glassing, then you'd have to draw them.
To detail armor, you have to build up some sections whilst removing material from others.
To remove material, use a Dremmel grinding stone or band sander depending on the area, shape, and contour of the detailing. Wear a respirator and eye protection while doing so. Be sure you reference a lot of pic if you want to get it "just right."
Bondo can be used to smooth the finished product and build up areas, but don't go overboard as it can add considerable weight to the armor.