ok, i'll give you some constructive criticism since its your second work:
* contrast, contrast, contrast - this picture lacks it and you could use tons more of it.
* shading. there is very little to this picture, so it looks terribly flat.
* background. doesnt need to be fancy, but the color of the current one is pretty much the worst possible match given the palette you used for tsunade.
* grey pixels. there should be none. unlock your layers and make sure you fill everything in. this comes with practice, and almost all rookies color this way and make these mistakes.
* details. look at tsunade's eyes. wtf is up with those eyelashes or wat should i call them? XD you would be better of with a much darker color.
also, pay attention to your light source when coloring.
then, all you need to do is mind the above and you should be better off next time. let it take a few times though, it comes with practice! dont be afraid to mimic others at first, its a good way to learn, but after you learn your way around coloring, originality is very important!
well, hope that helps! good luck!