Here's my complete workflow for creating a pixel art sprite from scratch, in case it's useful for anyone starting out.

I start at 32x32 pixels in Aseprite. First: silhouette pass. I fill in the pure black silhouette of the character with no interior detail. This forces the overall shape to work before any detail is added.

Second: color blocking. I pick three values for each color region — midtone, light, dark. No more. I fill each area with the midtone first.

Third: shading pass. I add the light value on top surfaces and the dark value on bottom surfaces, relative to a single light source direction. I don't change this light source position mid-sprite.

Fourth: outline refinement. I review the silhouette at actual size and at 4x zoom. The outline should read at both sizes.

Fifth: dithering. Where I want a smooth transition between two values and don't have enough pixels for a gradient, I use a checker dither pattern. At actual size it optically mixes to a mid-value.

Sixth: final cleanup and export. I export at 1x and 2x. The game engine handles further scaling.

The whole process for a 32x32 sprite takes me about two hours now. At the beginning it took six.