for chain mail it's best not to really shade, if you're drawin on a larg escale then try and draw the individual links of chain, it'll take a while but it'll look awesome. if on a smaller scall try and draw lots of little hoops (it doesn't have to be too accurate) then onece you've picked a light source shade the shadowed areas and recesses by shading over the hoops to make them areas darker. hope that helps.