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Cosmo: Let's start from the inside out. What should you have going on under your clothes to give you a sleek, smooth look?

Charla: Underwear is 50% of the battle. Obviously, a shaper will suck you in, but so many traditional ones are a turn-off because they're constricting and ugly. One of my greatest finds has been these "Skinny Britches" by Spanx. They're amazing, super lightweight bike shorts that come in a variety of really cute colors. You can wear one pair or even layer a few for extra compression.

Cosmo: Everyone worries about VPL, but in your book you take on the dreaded VBB (visible bra band) — that super gross ridge that forms when your bra is too tight and digs into your back. What's a way to eliminate it?

Charla: Get a professional bra fitting! So many women end up being a size larger in the cup and a size smaller in the band, and the ill fit is the culprit of the VBB that I talk about. Another little trick — if you're smaller chested, you can get away with wearing a shaping tank top (as long as there's lycra in it) in lieu of a bra.

Cosmo: Let's talk about actual clothes. You say it's important to make your body look balanced. How can someone who is top-heavy do this? And what about someone who's bottom-heavy?

Charla: You should always make sure that everything on the larger half of your body is clean and simple. So someone who is top-heavy should opt for a fitted v-neck sweater or cardigan in a pretty but subtle color (i.e. no screaming red or neon). A bottom-heavy type should go for something like a dark pencil skirt. Then you can play with volume on the other half — pair the v-neck sweater with a pair of wide-legged jeans, or the slim skirt with a more voluminous top.

Cosmo: A great pair of jeans is a staple every girl should have in her closet, but with so many options out there it's hard to figure out what to go for. What are the details women should consider when trying on denim?

Charla: A few denim rules that I think apply to every body: no huge logos on the back pockets, no super light washed denim, and keep the details (like rips and embellishment) to the bare minimum. While I'm a big proponent of trying everything on before you buy, in general dark denim with a little bit of stretch and a medium rise are the most flattering color, fabric, and fit for any woman.

Cosmo: To look thin, you say it's not just about wearing the right clothes — even your hair can shave lbs. off your frame. Can you explain how to get "skinny" hair?
Charla: I always say if you can splurge on one beauty treatment, make it highlights or lowlights. The last thing you want is a single block of the same color covering your entire head. Whether you're a redhead, a brunette, or a blonde — if your hair is all one shade, it's going to weigh you down.

Cosmo: And what about accessories — what are some that can add to a skinny look?

Charla: Definitely bangles — and since enamel ones are a big trend for the summer, use them to your advantage. Layer a bunch when you're wearing a tank or sleeveless dress. The eye will be drawn to your wrist — rather than to the upper arm, which is an area a lot of women are self-conscious about.

Cosmo: You recommend experimenting with different looks and taking pictures of yourself to see what's most flattering. Is a camera more honest than a mirror?

Charla: It's just a great way to see yourself from a different POV, and it has a more lasting effect than a mirror. Once you have a few skinny shots, save those looks on your computer, or print them out and paste them in your closet. It takes the guesswork out of putting together a flattering outfit.

Cosmo: Speaking of pictures, are there any poses to strike that'll always make for a good picture?

Charla: Step out with your right foot, and place one hand on your right hip so that it's not pressed up against your body. Make sure your body is slightly turned — you never want to face the camera dead on — stick your neck out, and hold your shoulders back.

Cosmo: The message of your book is to dress to look thin at all times — even on Sundays when all you feel like doing is throwing on sweats and a tee. What's a cute, comfy outfit to wear when you're just lounging around the house with your guy?

Charla: Yoga pants are great for this — they're super comfortable but still form fitting and sexy. Pair those with a long-sleeve cotton tee or a cashmere v-neck sweater. Not only is this a stylish alternative to a pair of sweats, but I promise you'll be much more inspired to spice up a lazy Sunday with your guy if you actually look and feel sexy.

Headshot of Jessica Knoll
Jessica Knoll

Jessica Knoll is the New York Times bestselling author, screenwriter, and executive producer of Luckiest Girl Alive—now a major motion picture from Netflix starring Mila Kunis. Her latest novel, the instant New York Times best-seller, Bright Young Women, is out now.