First think about what you want. Do you wanna look nice and attract people or do you want something comfortable that you can wear and not look like a complete slob. If you want to look nice and stylish go to places like the Gap or Sears and buy brand name things like tommy hilfiguer jeans and sweaters. You may not notice much of a difference between the expensive designer sweaters and regular stuff you usually buy but girls that know clothing will.
have fun.