Make it dirty. Lots of weathering and rust. And use metallics. Check out the work of
Allan C, some lovely Orks in that man\'s gallery :] Make the weathering oily, and include a very large weapon (metal fist/gun/über-claw-thingy). Banners strapped to the back also tend to work well with Orks. And you MUST include a Grot somewhere, on the base or ion the mini. Hope that helps
Cheers
~Bill