i suggest looking at lots of low poly faces their wireframe in Sketchfab and using them as reference
i suck at explaining my progress but here is a wireframe of the face, i use a bumpmap for the mouth, i stole this from Slime Rancher
for the hair i just used the smooth and hard edges, when i make hair quickly in low poly i make streaks with a hard edge
idk if this is helpful but ya i suck at this!!, i use Maya btw, i probably unlearned blender by now