Tigerblood said:
The best way I've seen a weathering technique is "color washing" the creases and beveled areas. Just youtube that for instructions. As for doing a battle damage for an Iron Man suit, what I've done was add round "dings and dents" to simulate bullet hits and some gouges on the parts before paint. I also used a chrome paint base (before you paint your main color) then used Vaseline on the edges and areas where you have the "damages" and then paint over it. Once the paint dries, you can just chip off the paint on the areas with Vaseline.