Asteroids are great for learning pixel art
Some advice of how to break the process down into steps below.
I recommend you save a copy (or layer) at each of these steps, and post them all for advice so we can see your process.
Especially if you feel like your unsure how to move forward, just post your progress.
Step1) Pick a primary light source e.g. a sun off to the side as is shown in the references.
You will probably also want a secondary light source on the opposite side but a bit more behind the object and something further away preferably a different colour. A secondary light source both helps it to stand out against dark backgrounds and gives you more to work with when creating textures.
Step 2) Paint some solid blobs
Step 3) Roughly paint the light and dark areas of the primary light source without any smoothing and don't get caught up in detail. You forms should look interesting before you move on.
Step 4) IMPLY some craters and texture by varying the line between the light and dark area. At exactly this point the texture should be MOST obvious. Do not get stuck applying this texture all over the rock. At this point we generally still haven't added any new colours.
Step 5) Now's a good time to think about that secondary light source and add some of that colour around the dark edge to further define your forms.
Step 6) Now we start adding 1 or 2 extra colours to the gradients.
A common mistake here is to evenly distribute the shades across the shape because you think this is how to make something seem round when in fact as per those references there is often only a thin gradient between the light and dark. Varying the thickness of the gradient along the line makes for much more realistic and interesting forms.
Step 7) Now we're pretty much at the stage of clean-up, smoothing, anti-aliasing and general pixel-level detail. Be careful not to get sucked into single-pixel noisy textures and detail.
GLHF
