Hello!
I noticed that of the 17 colours you have used, you have 4 flesh coloured tones (including the fleshy browns used for the eyes).
The lighter flesh colour is only being used in 4 pixels (the highlights on the hands). Why not try using the colours to their full potential by attempting some basic shading on the face?
You, the two colours in the hair are so similar it's hard to see any difference. Also, it might not have been neccesary to use a seperate brown for the belt, so you can remove those and bring the colour count down at no cost.
Also, try to think about where the light is coming from, and make the highlights consistently come from that direction.
Click here for an example of what I mean.
Good first step. Keep going!
adding to what gennoveus said I would also delete the white background and turn it to transparent or to a more neutral colour.
Also I would suggest to practice a bit before submitting pieces to the gallery. If you are looking for advice you can use the forums from this page or from pixelation.org