Welcome to pix!
Cool start man
Some quick thoughts on skullhead
Did nothing much, just desaturated the colors, did some structural fixes, established a light source
Hope that helps
Regarding your pixel "technique", I'd say that avoid all that noise. Strive for simple first. Go for CLARITY over DETAIL.
There's a lot of pillow-shady stuff going on like rimlights on on the heads. Think of the forms before thinking about the light and texture.
The bigger forms come first, then come the smaller forms on the bigger form like details and texture.
Keep posting more