Robit sprat

[GrooveMan.exe]

I'm going to be conceited; and post something I made.
http://groovemanexe.deviantart.com/#/d2zqjbz
Look at the helmet. See how because the metal parts are different sizes and curvatures, the highlight shapes are different? Note how stark the contrast is between the lightest shade and darkest shade.

1) Change your pallete first. Ditch that pure black; make the darkest shade even darker, and the lightest shade even lighter.
2) Go on TSR and have a look through the sprites (high-bit games like DS and PSX will have clearer examples). Look at how they shade metal, and deal with lightsources.
3) Using only the darkest shade and lightest shade, look at each section of metal plating at a time. Use the lightest shade in accordance to how it should catch the light. Rinse and repeat with every section.
4) Use the intermediate tones to flesh out the light and shadow; using them to anti-alias if need be. You shouldn't need more than 5 shades.

Edit: Also the lineart for those arms/hands are really lumpy/noodly. I would suggest redoing them.