Looking pretty decent, but I think there's a few major things that could be fixed:
• Not really specific to this, but you really shouldn't reference from pictures like that. It's okay to reference anatomical diagrams, or really good art, but not a mediocre vector piece with fairly poor stylizing. Always try your best to work from life/photos, grab some pictures of cats, and grab some reference of poses similar to what you want.
• The rules of drawing still apply, so remember to do some drawing studies of still life, of people, etc. This is just another general advice thing, and you may already do this but I figured I would throw it out there.
• It seems like you're thinking of things too two-dimensionally. You need to think about the form, lines are usually just an indication of either form, or a separation of two things i.e. negative/positive space. Your rendering/shading reflects what you're thinking about, which brings me to my next point....
• Think about where light is hitting, and how it affects the object. You're pillow-shading, and you're adding random speculars which make no sense. Fur wouldn't reflect like that, it's not that shiny, neither would a cotton/wool shirt. You need to think about shadows, and how the form turns away and towards the light.
• Her waist is a bit too skinny, her neck is a bit long, and her head is being cut off from her body. I've done some edits so you can see how I've attempted to correct these issues.
