How should I decorate my room? (teen girl)?

Get some wall murals (huge ones!) that spark your interest. To save space (& look cool) wall mount a flat screen tv. Below the tv you could put up a shelf to hold some girlie figurines, or sports memorabilia. The best improvement I did to my childrens room is took out the carpet & used floating hardwood planks. Touch it off with some fancy night light that has fish, fairies or whatever in it.