I'm painting 5 MkIV marines and a Contemptor pattern dreadnought. Here's how:
Undercoated black and then oversprayed with a rusty brown colour (bestial brown) and then given a layer of matt varnish (Testors matte coat). This is to seal it for the next stage where I gave it a spray of hairspray (any old cheap stuff will do!) and sprinkled some large grain salt over the model so it sticks to the wet hairspray. When dry, I then basecoated over the top of the salt with a brown/yellow and then a brighter yellow on the top. When dry, using my thumb I gently rubbed off the salt, taking the paint with it, and leaving the rusty colour showing beneath creating a GREAT paint chip effect! Here it is:
Realistic ruggedness or what?! More to come very soon!