Hi - how about making some diy art for one of your walls?
Get some remnants of fabric or an extra pillowcase/cushion the same as your bedding and use the fabric to cover some artists blank canvases - cut enough fabric to go around the back of the canvas and just staple it on. Have a look here to see what I mean:)
http://itswrittenonthewalls.blogspot.ie/2011/08/diy-wall-art-scrapbook-paper-styrofoam.html
Perhaps you might like a wall decal on the wall behind your bed either something flowery, or whatever you like or a wall quote? Have a look at these websites to see if there is anything you like:)
http://www.decalsforthewall.com/
http://www.wondrouswallart.com/wall-stickers/girls-bedroom
Perhaps you might one or two shelves to put some of your stuff on that you really like or use one to put some nice pretty boxes on in which you can put all sorts of things in to keep handy?
Have a look at these shelves and pretty boxes:)
http://www.pbteen.com/shop/accessories/shelves-hooks/?cm_type=gnav
http://www.pbteen.com/shop/accessories/storage-baskets-bins/?cm_type=gnav
If you get any of the storage baskets/bins then get some in the colour of your bedding etc.
Perhaps you might like a couple of these wooden letters - say, you could get with your initials?
http://www.pbteen.com/shop/accessories/wall-letters/?cm_type=gnav
You might like somewhere to put your make-up if you wear it and perhaps somewhere for your jewellry?
http://www.pbteen.com/shop/accessories/jewelry-storage/?cm_type=gnav
http://www.pbteen.com/shop/accessories/beauty-makeup-organizers/?cm_type=gnav
http://www.pbteen.com/products/metal-floral-beauty-storage-mirror/?pkey=cjewelry-storage&
A new ceiling light/lantern?
http://www.paperlanternstore.com/round-paper-lanterns.html
Anyway, hope like some things I've given you to look at above :)
Anyway, hope this helps:)