My technique would be to use thinned down Codex Grey to neatly paint the portions of the cloth where light hits the model. Make the edges soft. Then once it is well dried, use several coats of Badab Black Wash or another good black wash to darken the grey.
Example shown below of Commissar Yarrick:
The second picture was taken before I added to more coats of Badab Black Wash to the areas that needed it (mainly that grey stripey area below his sword hilt.
For the armor use a brighter grey and hit only the hard edges of the armor. Then for a select few edges that catch more light, edge again with Skull White or some other nice white. Remember to thin down your paints to a good consistency so you don't get paint flakes or caked paint on those edges. Don't put any black wash over the highlighted edges of the armor.
So your cloth areas will end up muted and soft and your armor/metal areas will end up with hard crisp lighter edges.