One of the more enterprising Seventh Avenue names, Diane von Furstenberg at twenty-nine is a fashion notable who's always commanded more than average attention. Her beauty book includes all the traditional departments--skin and hair care, nutrition, exercises, self-image--with examples from her own glittering life and references to ex-husband Egon, their children, Jet Set friends, and her heavy work schedule. Little is ""new"" but her forceful imperatives may indeed be this year's pet rock. Although she writes with conviction, there are problems of internal consistency: it's difficult to reconcile her emphasis on being natural, being yourself, with improvement techniques that range from regular exercise and judicious makeup to chemical peels, cosmetic surgery, and silicone injections. And after the insistence on doing these things to make yourself feel better generally, she adds this countering summation: ""Everything we do is for show."" Still, she sounds authoritative if a bit overdetermined for some tastes. Cut from the same cloth as the Sassoons--a prestige label for sure.