I first made the dark spots in the armour with several layers of Devlan Mud. Then high lighted the edges of all spots with orange and yellow... Worked out pretty good. I also used the Mithril Silver on few spots to make more damage look.
Marines head and bolter are taken from Chaos marine bits. Spikes on the left shoulder are from Orc bits. Rest is from tactical marine box :) I decided to paint the 5th company symbol on the bolter. Dust and dirt on the boots look different in the photo... Much more contrast than in reality... Maybe the flash light did it :)