Another tip is don't draw things straight on like that.
If u can, usually it's better to see things at a bit of an angle as that makes it much more 3d instead of looking like a cardboard cut-out.
Try drawing the same robot from a few perspectives and each time it will probably get better.
U can also use this as an opportunity make changes that improve the desig rather than limiting urself to an idea that wasn't first conceived in 3d.
Personally i like to block in a bunch of silhouettes, pick one i find interesting, then block in the light and dark to give form before proceeding any further.
Here's the early stages of a sprite to show what i mean.
This later went on to have fixes, colour and animation but not before i felt it was ready.