You just know that Rachel Zoë Rosenzweig was the coolest girl in school. The New York native not only has a roster of gorgeous young starlets seeking her styling services, her own glam-rock, 1970s style gets plenty of attention too. "I've stayed true to my style for 10-15 years", Rosenzweig says. "I've always loved that Boho, 1970s glamour; Grecian-influenced, big jewellery, that whole Halston, vintage YSL thing."

Rosenzweig moved to LA two years ago, when her styling work went from being based around fashion and music to dressing celebrities. "Even though I was living in New York, I was really living in planes and hotels," she says. "It was physically and mentally draining." She now has 10-15 clients, "depending on who has a movie coming out", and covers both women who have their own defined sense of style and those who need a complete fashion overhaul. "I've had clients come to me saying 'Help me!'," she laughs. "It's interesting to do both."

She and the client have an initial meeting where they discuss what it is they’d like to change, as well as what sort of look they are going for. “Most of my younger girls want to look like Kate Moss,” Rosenzweig explains, “or these days, Sienna Miller as well. When they’re 18, 19, they want to transform themselves into someone they admire.” Both Jessica Simpson and Nicole Ritchie can thank Rosenzweig for their recent, chic makeovers, while Jennifer Garner’s evolution into a bona fide Hollywood player (in the fashion stakes especially) is also Rosenzweig’s handiwork. The common denominator of her client list is young, beautiful women who are still evolving their own style (with the exception of Cameron Diaz and Kate Hudson, who could reasonably be said to already have plenty going on).

Of Keira Knightley, a recent client, Rosenzweig says, “She’s so gorgeous she can pull off any look, like her new short hair. Sometimes when these girls are unquestionably gorgeous they like to shake it up a bit and become a little more edgy.While Rosenzweig can reel off a list of designer favorites as long as your arm- Lanvin, Rochas, YSL, Valentino, Balenciaga, among many others- her first love is vintage. “Oh please, I’m the most vintage-obsessed person in history,” she laughs. “I collect designer vintage. I’ve got to stop.” Many of her clients end up in vintage on the red carpet: “it’s the only way to maintain individuality.”

A common gripe of many stylists- that they have to fight for runway ready-to-wear with every other stylist and fashion editor in the country- is familiar to Rosenzweig, who says the other problem is “by the time your client wears it, everyone has already seen it in the magazines”. Apart from vintage- which she sources at LA favorites Decades, Resurrection and The Way We Wore- she visits the couture archives of the big design houses. “And I’m a huge jewellery person,” she says, claiming the fixation comes from her mother, who has “a jewellery collection like you’ve never seen. The great thing is I can steal pieces and she doesn’t even notice they’re gone”. While she laments that the last few years have seen a shying away from jewellery at awards shows, she declares, “I’m going to change all that”.

While Rosenzweig might be the new kid on the block, she’s already racked up some impressive fashion moments: Kate Hudson at the Venice Film Festival in a sheer, two-pieced Chanel couture number, flaunting her five-month pregnant belly; Cameron Diaz in white, strapless Louis Vuitton at Cannes, Jennifer Garner in a one shouldered Valentino at the 2004 Oscars…This last awards season alone, Rosenzweig outfitted Mischa Barton, Portia de Rossi, Jennifer Garner, Julie Delpy, Salma Hayek and six other women (for the after parties).

“As much as we might complain while we’re doing it,” she explains, “I wouldn’t trade it in for anything. The day I feel like that is the day I leave this business. You can’t work this hard and not love it.”Rachel Zoë on…

Wardrobe essentials: We’re never going to stop seeing jeans. That sounds so basic but it’s true. Designers have mastered the art of denim, and these days everyone can find a jean that looks good on them. Also the little black dress. It’s flattering for everyone, particularly the 1950’s cocktail dress.”Overrated trends: “No more jeans so low you can see your butt crack. And the really sequined bolero; certain ones are still OK, but not the ones that are in every store.”

Greatest fashion crimes: “Wearing things for the trend and not what works for your body. Not layering things properly- like a sheer dress that isn’t lined properly. Too many prints. And the wrong hair and makeup- when it doesn’t work it can make it look like you’re wearing a costume.”How to always look your best: “Always wear things that you feel comfortable in, stay true to things that work for you. If it’s not right on you, it’s going to show.