It's more of a comment for the edit, but no one should use outer AA unless there is either a fixed background or you are 100% sure the picture will stay on a background where the AA itself works. Otherwise it will look like crap. If you want smoother results on an image with transparent background, either play with alpha transparency or with line width and 45°angles, but never outer AA.
The main problem with the original one is the harsh contrast between the dark and light colors, thus making the picture look jaggy. Either AA the lines, use a lighter color for the lines, or use darker colors on whatever is surrounding them. Many of the colors could be reused to come up with better results.
The palette itself is rather boring and monotonous. Look at Kcilc's edit and see how he uses yellows and blues, and not just plays with brightness.
While you have some idea about lighting going on, I suggest you to try and give the face volume. You know, eyebrows and cheeks and the like, and try to show them through lights and shadows. Again in kclic's edit you can see how he tried to address that.
When coloring, don't just lay colors etc, but try to give the picture personality, and bring some character. While it sounds abstract, if you have a mental idea about how the thing you are coloring is, you will be able to pull better results.
I might try to color the lines at some point, but yeah good luck with further edits.
