There's some steps you should take to help you with this.
A. Find your own style (girly,prep, scene ((google it)), hippie-style, etc.)
B. Look around the mall and whatever stores suit your style ^ go for it and find stuff you like.
C. Forever 21 has stuff for everyone.
**Tip: Look at Seventeen Magazine and find outfits in there, and go to http://www.polyvore.com/ and search your new style for ideas**
Hope I helped. --Dee