well said InRem.
the best technique i have found for chipping/scratching the paint on clones is using an exacto that isn't quite as sharp as it used to be...you all know what i mean, the very tip of the blade broke off, that sort of thing. of course you have to be careful, but small strokes produce little scratches while scraping takes off a bit more, i think everyone gets the idea.
depending on how movie accurate you want to get Phruby, Cody had 2 pretty pronounced gouges/gashes on his chest armor, near his rank badge, you can see them in this photo below.
as far as weathering, i would do a brown/earth wash on his lower legs and a lighter wash as you move up the body. something to make the white not so white, but still more subtle and movie-like. i personally don't care for heavy washes and dry brushes on the clones, they were dirty sure, but not so flithy the armor was black/grey ALL over. i guess i just don't care for over-weathered clones, it's kind of a pet peeve of mine.
i tend to use a type of dry brushing for the black "scratches and dings" for lack of a better term. i suppose they are more like blast-marks. anyhoo, i like to get the paint where it just starts to get gummy, not dry but not wet totally either. using an older brush, i push down and pull up to give random blast mark damage, some large, some small and some darker and more pronounced. i like the look of it, along with a few light brown marks done in the same manner for a little dirt here & there, but again more subtle. i think everyone saw how my clones turned out in my customs thread.
i just got my Neyo & Cody kit from Bantha5 and am working on Neyo at the moment. i had to run to micheal's and get a new small detail brush, Neyo's visor is a bit of a pain to get straight