Serena's style is made up of a lot of different elements. When she's going to a party she completely dresses it up, with studded jackets, bandage dresses, and sequined skirts. Other times when she wants to be casual she just wears a simple coat with a chiffon blouse and jeans. Usually her style is boho chic with flowy tops and layered necklaces with feathers.
Blair Style ; http://www.polyvore.com/blair_waldorfs_style/collection?id=3441699
Jenny Style ; http://www.polyvore.com/cgi/collection?id=3441677