as RedAssassinZero said, it could use some work.
the lines are rather rough, so try cleaning them up and making sure your lines are smooth and clear.
the arms and legs are disturbingly skinny, even for manga/anime style (okay, actually, i can't really say that. i do that on "chibi"ish style stuff as well, but it really depends on the style). also, the arms are bent kinda oddly. they look more like rubber/noodles than actual limbs.
this isn't quite as important, but how strong/dark the lines around her chest are is kinda strange. it ends up drawing the eyes there because of the contrast against the lighter values of everything else. also, the chest doesn't bulge out to the sides quite so much. or so i think. if you look in a mirror, your chest should be sticking out towards the front, not quite so much towards the sides. of course, it would stick out more if you're looking from an angle.
umm besides that,..shading is always nice
smile takes some practice, but yeah. at the very least, proportions+clean up your lineart. that's always good.
if you want to be doing paid artwork, i honestly don't know how good your stuff should be. i'm not dedicated enough to bother with that, so i just stick with free stuff in spare time. if you wanna see what i've done:
http://s1281.photobucket.com/albums/a515/soojinrl/Gaia Art/
not so proud of some of them, and style varies through the pieces.. most capped at 2hours of work/piece. only have 5 up since i only started doing this a day or two ago ._.
tl;dr- clean up lines, work on proportions of limbs+chest, possibly try shading.