New to pixel art/art and need help to understand banding

[Ymedron]

As a small note, the teeth don't actually have to be white. They can be kicked down to a darker gray, or preferably surrounded by darker pixels to point out the edges of the mouth.
Right now, the only way I know that she has her mouth open is because of the red lips and the black spot.

However, don't just draw the lipstick all around the mouth, I have a feeling that's not going to work so well. !

[Kelmaro]

So came back to post my most recent version, and ask weather or not there is still any major problems with this. Mainly would like to know if the arms or teeth are still a problem. The teeth I didn't change much but I made them a bit darker and the skin darker.
Though overall I'm pretty happy with this but any critique I believe would still be good to hear.

also would like to hear any critique on the gun or hair.