I'm going to start with the coloration on this piece.
The color scheme is OK, other than the rainbow lightning bolt and pencil. They seem too out of place, considering everything else in the piece fits with the same hues of black, blue, white, and purple.
There is a lot of white space to the right. Don't forget the elements of art and principals of design when creating art. Something could have been placed in that white space to balance it out, such as text. It could also help to create a background and have some sort of object on that side.
The pencil, which is somehow sticking to the ear by some form of witchcraft, is much too big. The eraser looks like a lump of plastic held on by a piece of very dark duct tape. I'm not sure what the silver and blue glowing disk glued to the edge of the ear is supposed to be. Considering it's attached to the oddly-shaped cord running down to the little black square, I'm assuming it's a headphone. Why is it placed near the ear, and not inside it? Is it a special type of earbud meant to double as a giant glowing earring?
Is that oddly-shaped gray square an iPod Touch? The screen is very crooked. The edges of the object are also uneven.
Is she wearing swimming goggles around her 'neck'? Ones that are so small they could never fit over her eyes?
The jacket is one big mess. The edges of it, such as at the sleeves and bottom, are jagged and unnatural-looking. The decal on it, that RiverClan symbol, doesn't fit with the curve of the clothing. It looks pasted on. The pockets on the jacket look like foam pieces. What is that odd square edge on them? The silver D on the left sleeve is almost in perspective. It could use some more warping to make it appear to go with the contours of the sleeve.
What is going on with that iPod? Is it swinging? Is it a magical floating iPod? The iPod at rest should be closer to her body, not all the way out there.
And now, anatomy. I could go on for days with this topic. I'm going to start with the tail. It's oddly shaped and appears to be broken near the base. It also appears to be emerging from the side of her leg. The area where the fur puffs out looks odd.
A cat's ears do not work that way. Remember: cat ears are rounded at the end, not sharp like a knife. Someone could poke their eye out on that thing.
The other ear is also drawn out of perspective. By the way it is drawn, it is nearly on the back of her skull.
Her left shoulder (the one with the cloud) looks broken. Her arm is also too short. When drawing anthros (or whatever these are called), remember to think of human anatomy. The tips of a human's fingers reach down to the thigh. A diagram may help, such as this one: [link]
The other arm (to the right of the piece) also looks broken. It is bent at an unnatural angle. The shoulder is also shaped oddly. Cats do not have five 'fingers' in the spot you placed them in. The fifth 'finger' is placed much lower down.
I'm not sure what's going on with that chest. It looks like there is only one breast, and it's too far off to the side. There is no shading at all to indicate the place of the other breast.
Based on your location of the left eye, the right eye should be appearing. I'm not too sure what's going on with the upper lid and the eye. They look like they're detached from one another. The nose, because of its lack of any shading whatsoever, looks like a black piece of plastic shoved onto the face. The hair/bangs/unnatural puff of fur appears to be made out of metal. And that metal is covered with small droplets of water. The edge of the hair is too sharp. Like the ears, someone could poke their eye out on that thing.
Unlike the previous piece I critiqued, the shading on this one doesn't appear so rushed. The shading could still use work. The feather lines are obvious in many places, such as the left arm. It also isn't shaded correctly. Notice how you can see the base color of the sleeve near the edge. The shading on the right breast looks oddly placed. I can also see spots where the shading goes outside of the lines (the bangs/hair). The places where shine was used often don't make sense.
Keep working at improving, and in a few years, I'm sure you could redo this piece and have it look much better.