looks pretty simple,
i aint no expert on pixel art or portraits for that matter

but your head looks like a pentagon, the mout looks like your just about yo open your mouth for a whiff, i cant do that AA stuff so all my pictures are transparent/meant to be, and you need to add more color

study up on your AA (anti-aliasing) before doing something like this. also...you used gray on yellow, which makes absolutely no sense at all. add contrast by using a variety of darks and lights rather than colors that have almost the exact value. eyes arent completely blue...unless you bought some cheap contacts, otherwise, you have white around your eye. also study a bit of anatomy to get your jaw/nose/forehead/eyes/mouth/etc. correct. good luck with it.