My basic idea: Since the description was about a robot, I wanted to draw something in that direction and decided on a kind of cyborg hybrid.
For my sketch, I first considered a general character. Although I have paid attention to proportions but things, such as details and the background moved.
Once you are satisfied with his sketch, you can draw the lines new, cleaner. For the outlines you just have to create a new layer.
Some prefer to draw everything with thin black lines, but I prefer to use the matching colors (but you should be careful not to use the same color as to fill in).
When coloring I use a base color, From this hue I choose a lighter and a darker for the shades, which is why you should not choose the root not too dark (see Figure 1) but rather a color that still allows room in both directions (see picture 2)
Details (Light / Treasures etc)
To watch. As I said, I usually choose a medium hue, not too dark and not too bright. But before you draw the highlights and shades, you have to think about where the light should come from.
The following pictures show my process of shading the knife, the tonfa, the breastplate and the mask.
Basically, the following applies: 1. Basic tone 2. Dark shading 3. Lightening tones 4. Transitions for a more natural look.
For the mask I also added a blink for the "eye". For that I used the spray can tool, put it in white and set the opacity to 20%.
In general, a soft brush or soft spray cans for color effects and to create transitions.
In the last picture you can see a dare light course as it would be possible.