You know her. That glossy girl who always looks hatefully perfect, no matter what the occasion. Meanwhile, you spend every morning furiously picking through a pile of trendy castoffs before giving up and settling yet again on your Seven-jeans-and-black-turtleneck uniform (yawn). The editors of sister publication INSTYLE feel your pain and have compiled INSTYLE Secrets of Style, A guide to dressing that is brimming with both practical tips (''When trying on a wrap dress, it's crucial to bend over. One strong wind could leave you more exposed than you had planned'') and glamorous role models (Cameron Diaz and Heather Graham are featured in the ''Great Moments in Boots'' section). The pictures are pretty, the advice sensible -- this is a fashion guide that will stay relevant after the voguing has passed.