School Baggy jeans, plaid flannel shirts and Doc Martens shoes are in style this season for back-to-school fashion. p Choices Multile SUZIN BODDIFORD SPECIAL TO THE JEWISH NEWS IA/ PHOTOGRAPH BY CRAIG TERKOWITZ hen it comes to the hippest homerooms, this fall teen-agers make the fashion grade by dressing every which way. It's time to break those rigid rules and throw in a little attitude for extra credit. That's the trend senior wardrobe stylist Jimmy Hanrahan, who interprets fashion for 55 million young viewers on MTV, is pushing. Whether he's dressing a funky video jockey or outfit- ting a popular musical group for its latest video, the key is indi- viduality — "taking the trends and twisting them around so that they work on you, and not because it was dictated to you in a magazine or on a famous celebrity," he said. Hanrahan's single favorite pick for fall? "A great white shirt," he enthused. "It's an inexpensive fashion fix that anyone can in- stantly personalize." The most important new trend in student-wear, according to Joanna Corsara, junior sportswear editor for The Tobe Report,