Okay now for some comments and crits, okay my first thing would be to say before you colour start by tidying up your lines you have obviously done this to some extent but rough lines always detract from the final image. I would suggest (if using photoshop) to zoom in a lot and make sure each line is as good as you can make it but keep zooming out so you dont lose the feel for the whole piece. The alternative would be to ink the lines using a program like Adobe illustrator which will give you crisp lovely lines everytime! Check out my thread Chrono Crusade Lines for an example. As Jats shows you can also ink well in Painter see his thread for an example.

Right so now your lines will be looking spectatular i will go onto the composition. The jaw line starts far to high bring it down to around the same level as the bottom of the nose. You also have no ears! from the shape of the hair in my mind at least you should be able to see some ear! The mouth is too wide, make it about half the width. Onto the eyes, your irises need to be rounded off they are too large on the right side remember your pupil is always in the centre of the iris so it shouls be the same distance from each edge. Where the speculars (the light refecting on the eye) meets the white of the eye either remove the line defining the iris or make it segnificantly thinner. The specular should also be more rounded at each end making it more circle than quadrent.

More definition in the hair would be nicer, and it should go over the eyebrows not the otherway round!

Okay the colouring you seem to have gone for an almost cell shading style on the face with a large colour difference between areas and a softer shading style on the hair. Try and keep the shading style consistant through the whole piece. For general shading tips see Bomu's tutorial this gives you some good staritng points for airbrush pressures and other settings.

My only other suggestion will be to make sure you work at a suitably high resolution 300dpi minimum really so if you were scanning a piece of A4 that would give you a canvas about 2480x3510 pixels. Rememmber its easy to shrink it afterwards you will always lose quality making it bigger!

I hope my comments have been useful to you and as most people will say the only way to get better is to practice I hope to see more of your work!

Here are a couple of links for inking lineart which have been posted on this here forum before, hope they help if you decide to try it.