TTNG_Mini_Celeste

You have the basics of pixel art down already. There's a couple of misplaced/overlapping lines, you wanna avoid that. Try to make the lines as crisp and clean as possible, in sai it shouldnt be too hard. I use paint.net for pixels so idk.
The hair shine feels stiff, could be more flowey.
Although I still dont follow this rule most times, start sketching/lining where the hair parts would be. On bangs like that its usually a small circle towards the top. Some hair styles I have no idea. If you start with the bangs then have where it parts set mentally.
The third shade color, on everything, can act like the lighter shade. Do the basic shading first, and the third shade can fill in half of larger areas. You can do more than just darker shade around the lines of the hair, for lack of better wording. Since youre also not going too crazy with it, the larger the pixel art the lighter the shading can be. On tiny pixels they can take like 20 shades darker on the third shade just to show.