First of all, Nina struck an excellent balance between emphasizing the importance of personal style and recognizing that fashion is at heart a bit frivolous - she doesn't take her subject matter too seriously, and for me, that's what set this chic little volume apart from the masses of fashion and style-related books.
Some of her excellent advice includes the secrets of style icons through the ages (ranging from Audrey Hepburn to Debbie Harry), fashion tips from designers like Carolina Herrera and Roberto Cavalli, how to edit your wardrobe so that it only contains remarkable pieces, and the power of a great pair of heels (which is something I certainly agree with). However, her most important - and most basic - advice is simply to wear everything with confidence. After all, "confidence is captivating, it is powerful, and it does not fade - and that is endlessly more interesting than beauty."
If you want to know more, you'll have to order the book.