So I'm working on that IG Valkyrie I posted up there, and I decided to try some chipping medium.  Chipping medium is a layer you apply on top of one layer of paint, then you apply another layer of paint over that (typically a different color), and then you can use water to create "chipping" effects to look like wear and tear.  I've never really had a great deal of luck with chipping medium.  I tried applying it through my airbrush, and although it seemed thin enough on its own, it kept clogging my brush.  Even after applying thinner at a 1:1 ration, it gave me problems, but I was able to cover the model.  
1.  White prime. 
2.  Dark Aluminium from Vallejo
3.  Chipping Medium
4.  Haven't decided exactly what color to paint this thing yet.  I should decide soon