The most important advice I can give you is that this is too big of a size for pixelart. It would be too much work to make it look good!
You could instead create the graphics of your game in another medium, either digital-painting or vector-based (latter might be harder)
If you insist on doing it in pixelart, you should reduce the size (to around 64x64) and duplicate or triplicate the size of the in-game screen.
^ Yeah what he said.
Decided to have a crack at a simple robot since I never done it before...
Here's the steps I follow (some stuff done a little out of order):
- Fill canvas with mid-grey to ensure colours will hold against a variety of backgrounds. Rough out an interesting silhouette - tried to get a loose pose with good balance, thinking mainly about the spine at this stage.
- Pick a light source (top left here). Block in the planes of light, dark and mid. Its recommended to break things down into planes first, even for organice shapes. For this I wanted to keep the shapes VERY simple. You do not need complicated shapes to make a good looking sprite. I'd advise keeping everything as simple as possible at first and work your way up from there.
- Balanced out the brightness of the colour ramp and rough out some highlights to better define the light source and the edges of the planes. Here I'm thinking about the material I'm working with and the light-source involved. For a dull metal like this I didn't want it to be too shiny, but still to have a subtle specular in places.
- Pixel-level work. Here I'm concerned with clusters, avoiding ALL pixel-level noise possible. Notice I do not concern myself with details, but where I can I add suggestion of lines for joints and stuff. If you can't work details into your small sprite then just forget about them and worry about blocking in each form with the right overall brightness. Clusters is something I'm still learning but notice I intentionally avoid adding a gradient on the rounded arm for example. Rather, I'm not worrying much about the contrast between groups of pixels. This contrast in fact is an important tool. Again, DO NOT get caught in details at this point.
- Finishing touches to pixel work. Add darker outlines around the shape. Notice the outline in the lighter areas is brighter than outline for the dark areas, this is fairly common these days. It is not important that every pixel is outlined, notice a missing outline pixel on his hand for example because I thought it looked better that way and there is enough other outlines to support the shape.
Added selective anti-aliasing, being careful not to overdo it or it will give everything a dull, blurry look. - Now I thought the ramp was a bit boring so I've tweaked done the mandatory step of adjusting the hue of the highlight to be warm, getting cooler through green and down to bluer shades in shadowy areas. I leant towards purple for the outline though so he wouldn't blend against blue sky for example
- Trying out some more interesting colour scheme. If you use Photoshop, bring up the Color Picker and eye-drop the various shades and see how the hue shifts around. This is something I'm still experimenting with myself. Experimented with a dark red outline and upped the saturation a bit thinking it would help him pop.
Sometimes it helps to add a secondary light source such as a red background light, or the common blue sky ambient reflection.
This can really help define your forms, though game sprites are often better with a single light source so they fit into a variety of backgrounds.
So I'd probably advise to think about that when you start designing backgrounds.
