LOS ANGELES — Erin Wasson knows a thing or two about how to make a vest look cool. She's been the stylist for the past two runway shows from Alexander Wang, a young New York designer making his mark with smart, moody sportswear.

For the fall show, Wasson threw a longer, unbuttoned vest over a baggy white T-shirt (teamed with skinny leather pants) and paired tight, buttoned-up vests with a black miniskirt and raggedy cutoff jeans.

For spring, she teamed a boxy gray vest with a pair of bloomer-esque black shorts. In both shows, the structured pieces look effortless — in that Kate Moss/Charlotte Gainsbourg "Who, me?" way.

Wasson is also a big name in the modeling world and has walked the runways for Proenza Schouler, Ralph Lauren, Balenciaga and appeared in campaigns for mass-market biggies such as Victoria's Secret and Maybelline. And she's a girl-about-town in L.A. — she also lives in New York — and frequently pulls cute vests out of her own closets to hit the scene.

"I always thought of vests as a version of the cardigan," she says, "another way to layer up your look."

Wasson favors a fuller-cut vest but doesn't dismiss the mini-vest (one that looks two sizes too small and sometimes doesn't button) sweeping Hollywood. Either way, the bottom of the vest should just about meet the waistline of a skirt or pant — or dip below it. (The days of wearing a shrunken vest over a long, untucked T-shirt, a la Hilary Duff, are over.)

"I think a vest looks better when you wear it with a V-neck," Wasson says, "It shows off your collarbone and your cleavage, if you have it — which I don't."

And forget about overpriced designer tees. Wasson is a fan of the Hanes T-shirts you buy in a three-pack to wear underneath (tuck them in if the vest is shorter). Roll up the sleeves and it looks a little undone, like you're not trying too hard. Or just wear the vest alone.

"I love the look of a vest with nothing on underneath. The parts of the body a vest shows off are things that women should be really stoked on."

Wasson likes the contrast of a suit vest with street basics. "A classic button-down underneath gets a little too preppy for me," she says. "It seems a little too contrived. And I'm not a fan of the tie.

"A great scarf is much cooler and a little less done-up. I don't think everything should be a total look. Try to find something a little quirky.

"If it's too much of a uniform, change it up. Take the pants you're wearing off and throw on jeans, or throw a denim jacket on over the vest. Take the unexpected and throw it on."

Wasson favors chunky, vintage costume jewelry such as oversized rings, thick bracelets and quirky, organic-looking metal pieces. "I've always been inspired by tribal, armor, organic and Deco designs, but if I wear a necklace, I keep it to just one."

Wasson found one of her favorite vests — a men's black waistcoat covered in metal studs — at a Los Angeles thrift store and likes vests of all stripes.

"I like a proper men's pinstripe, but I'm even down with an Indian-inspired Aztec print," she said.

But if you're going loud on top, keep it quiet on the bottom (and underneath), with basic, solid-colored pieces. Layering a patterned vest under things is another way to go. "I think the trick to making that work is when only a bit of the print pops out, just enough to add contrast."

Pencil-skirts and long, voluminous (even hippie) skirts are two favorite pairings. "Just make sure you don't wear a short skirt, or you'll look like Britney Spears — like you have on a naughty schoolgirl costume."