It looks pretty good, but I'd suggest using a pencil brush instead of the airbrush for shading (if you look at anime stuff, they always have that really harsh/sharp edge on their shadows). Going over your lineart once you have it on the computer would look nicer too (so it would be smooth). Right now the lineart is a bit messy and broken up. Using duller colors for the character (hair and outfit) would probably look nicer as well. The really intense (almost 100% pure) shades like that are sometimes painful to look at. Also, using more than one color of red would make the image more interesting (for example, you could keep the horns bright red but then the barrette in her hair and her shirt could be pinkish dull red or a darker red). The only place I think that bright/super intense colors are good are for the brightest highlights on an image or for eyes.

Sorry to say, Im one of the poor hobos that doesn't have a scanner and has to take pictures of my drawings. *cri cri* But thank you for the advice, I'll keep it in mind.

Yeah, I have to photograph pictures sometimes too because the paper is too large for my scanner. If you really want to keep your original lineart (instead of re-drawing it on the computer) draw it with dark market or nice pen (some shitty pens can really mess up a drawing. Usually even cheap bic pens are decent enough to draw with thankfully). Also, once you get it on the computer playing with brightness and contrast can help you get smoother linework as well. Usually doing art in a pen is all it takes though.

Also, do you know about setting your picture to multiply mode and coloring on a layer below?

Yeah, that's what i've done for the shading of the hair (Darker shading).

Yes, but if you take a photograph you can set that to multiply mode so then white and grey areas are mostly transparent and the lines stay black. That makes it really easy to color pics done on paper. That's what I was referring too.

......I love you. (Brofist type of way.) But how could i do that using gimp? Sorry for being slow.... ;c
EDIT: Nvm, found a great way to create lineart.

Glad you figured it out:) I was really excited too when I first learned how to do this.