This is sexy but the lady needs work.
I find that the hair color is too close to the NG page default color. That's the problem with dark colors and then exporting as a PNG. If you had applied the same technique you had with jeans and made a light outline, it would not have vanished so hard into the background. Any kind of shading and highlighting at all would have been nice on the hair.
The ass is not bad, but I feel more attention should have been paid to the the lighting. Where is the light source in this shot? It's difficult to tell when you light up the middle of her ass and then shade the top and bottom . Perhaps next time you should choose the direction of the light source and shade accordingly, because this way makes it look like you're not thinking about it.
The star and W on the cheeks are not as rendered as they could be. Easy fix, just take more time on it. And when you are drawing the pockets, it looks bad to just draw outlines and not shade, it keeps the pockets flat when in real life they would clearly drop a 'bit' of a shadow.
I feel like the ass was the only thing you had in mind on this piece. While it's a good ass, it doesn't help when everything else does not meet that same standard. The girls hair and remaining clothes do not have nearly that level of detail.
I find the colors not staying within the lines distracting as well. It makes it seem rushed.
Do keep practicing.