OK, i'm probably going to furry hell for this, but I felt I should try and show you where you're going wrong. I redrew the picture side by side so you can see the changes i've made. Excuse the crappy drawing, photoshop is running like a slug for some reason and i've just gourged myself on doughnuts and icecream which isn't helping, haha.
I've probably got it all wrong so if you guys wanna chip in, be my guest.
OK, so here's what I changed:
1) I made the head a little bigger and the body a little smaller. I tried to inject a little more cuteness into the character as she was looking a little rough looking (i.e. like she was gonna use you as a punching bag, lol). This is only a preference mind, not everyone wants their characters too look like eternal preteens, but I think it worked well.
2) I added a little more volume to the hair. One of the most noticible things at first glance, I wanted the hair to say "look at me!". That being said, I screwed it up a little, ha. Also I made it a little more wavy to add some character to it.
3) Reworked the face a little. I kept the basic shape which looks cute, but I moved the features closer together. They were spaced out a little too far for my liking. I also curved the eyes because the lack of eyebrows made her look angry, and did an anime esque wink for added 'kawaii'.
4) The original figures pose is arched kind of like she has a bad lower back. Shift the head over the neck, move the right (her left) shoulder down, and push the waist forward a little. She's not that dynamic, just enough to give it a natural look.
5) I'm not a big furry fan, but I think the tails look kinda cute, but exaggerate them a little. I made mine bigger, and more dynamic, coming from the back into the front.
6) Do something with the hands. Like I said last time, you need to add a bit of flavor to the arms. Don't have them both holding onto the bag straps on every character. Don't have them at the side all the time. Arms and hands are incredible tools to give life or meaning to your characters. A lot of body language is expressed with the hands, so use them!
7) I took off the muscle mass and replaced with with an a-typical anime body. Cliche, but it works. Lower the breasts to stop them from looking like pecs.
8) Add life to the clothes too. The little details count. Add some shading here, some details there. Give the shirt a little art design, even a strip (which i've used here to accentuate the body lines). And if you're gonna go for the open midriff, make sure it's worth it. Too little and it just looks like her clothes don't fit.
OK, so tell me what you think, if you have any questions, and tell me if i'm talking out of my arse, lol.
All the best.