Add some hair under his helmet

Shading for his head under the helmet, use ellipse of darker color than skin gradient/no gradient

Make him some shoulders, simply add another joint to his torso is aight

Make his hands thinner than his clothes so it doesnt look like clothes are stuck to his arm (optional)

Make the color of the front of his arm lighter and the colors of the back of his arm darker
Same goes with his legs
To make the parts look more distinct