Honestly, you've got a long way to go. Try looking up some guides on deviantArt about anatomy. Also, hiding her hands behind her back isn't going to help you get any better at them, you need to practice those, too.
In order to learn anatomy, don't try and reference anime. Reference real people, muscle guides, etc. You need to learn the original form before you try to stylize it, and in this case, you need to learn about real people before you can make elongated cartoon versions of them.
Keep trying, though! With practice and determination, someday, you'll be great (:
Here is one of my new pics I did for avi-art http://the-dark-distance.deviantart.com/#/d4yfq43
Again, keep in mind what I said. Try to learn about real people before you stylize them.
Oh, it was just avi-art.
Even when drawing cartoon characters or avatars, you need to keep in mind proper proportions.