Thank you very much for the help, I'll keep all that in mind.
 

Always nice to see new people getting into pixel art. :D

It's a good start - but I'd recommend increasing the contrast in general. The hair in particular has a good amount of detail, but the colours are just too similar to see it. I'd also say that the shirt could use one more colour and maybe some more texturing. I made a quick edit to show just how different the hair can look with a little bit of increased contrast, but I also added a little texturing to the shirt (dithering probably isnt appropriate here though, but again I'd add another colour).

http://imageshack.com/a/img845/2121/o1by.png

Other than that I'd say decrease the colour count of greens on the eye (far too many colours, and again - the difference isnt very obvious), and smooth out the hair a little more (there are a couple of jagged-y bits that could use a little editing. Apart from that though its not bad. Good luck with your future stuff. :)