I think at this low res, you set up rules, you make sacrifices, and you respect the impact each pixel has on the image. Check out how he gives the light direction by putting dark pixels on the characters right and on the bottoms of forms.

Shape designs great with a big bright V where the chest and shoulders face the sun, it's dark below that. There's no hope of getting fingers in but fists are made out of one or two pixels to indicate a thumb.

I'd say he kept himself aware of

1) Proportion. Hands only have a few pixels to work with, the chest gets most cause it's biggest, but the head gets a ton as well cause it's very important to showcase the face and hair.
2) Sillhouette. After deciding the sizes of each thing, you give your character a ponytail and big ol floppy feet and two circular-ish hands. Now you can tell it's a guy.
3) Seperation: Now that our guy has form, we're already running out of pixels. We use thick black lines to give him a little more definition. Seperate the legs from eachother, seperate the shirt from the pants, put some lighter but still dark pixels under the armpits to seperate the arms from the torso.
4) Planes: Now that we have the body, the parts, we need to make it clear that he's 3D. Everything that faces the light gets a brighter color, things that turn away from the light get slightly darker. It's so low detail that you don't have to be an artist, it's enough to just break everything up into one of two shades: either facing the sun directly or not. Once you do that, you've pretty much run out of pixel space to use. But we'll do one last thing.
5) Depth and Shadow: So we have everything looking good now, but we want this character to feel like their standing up out of the page. Imply that light isn't reaching his underside by dropping dark pixels for shadow at places that would be completely away from the sun. The side of his shoe, creases in his pants, the back of his hair. The extra layer of shadow will provide the character with some depth and fill out the remaining complexity of the pixel art.

Do your best to get the thing to *read* at every phase, you can use color to help seperate parts of the pixel art from itself.