As the owner of New York City’s intimates boutique La Petite Coquette, Rebecca Apsan has been boosting bods for more than 30 years. The self-proclaimed bra whisperer dishes on what lies beneath.

Where do we go wrong with our undergarments?
Women cling to their old bras like a baby would to its blanket. If the back is riding up and the straps are constantly slipping off your shoulders, it’s time to toss it.

So how do we know whether a bra fits well?
Slip your index and middle fingers inside the back of your bra while it’s on. You should have a snug fit. If you can’t get two fingers in there, it’s too tight; if you can fit a third, it’s too loose. Also make sure that the center of your bra, where the cups meet, sits flat against your sternum.

How do you keep bras in good shape?
Keep four to six bras in rotation per week. Do not wear the same bra two days in a row, so it has time to air out. Hand-wash bras after two to three wearings using Le Blanc Silk & Lingerie Wash ($16; thelittleflirt.com). It’s extra gentle.

When should you splurge on lingerie, and when can you save?
Invest in beautiful sleepwear, like a silk cami-and-shorts set. You don’t have to spend a lot of money to get a great bra. Timpa’s Duet line has inexpensive options that flatter small chests, and Chantelle makes the most supportive bras for larger cup sizes.

What’s your biggest undergarment pet peeve?
American women like their bras to be utilitarian: nude or black and very functional. You should see the gorgeous, colorful bras women from Europe flaunt. Have a little fun, for goodness’ sake!

What tips can we pick up from European women?
Whether you’re going to an affair or having an affair, you should always let a bit of beautiful lace from your straps or your cups peek through. Just a little tease—leave the rest to the imagination.

Do you help guys shop for their partners?
Men come into my store all the time to fulfill their own fantasies. If they pick up an item and can’t tell me if their partner loves the parts of her body it will highlight, I send him home. A woman has to feel confident to feel sexy.

OK, tell us your best insider underwear secret.
If you know you’ll be having your picture taken and you want to wear light clothing, choose black instead of nude shapewear. Black repels the flash so it won’t show through.

The Lingerie Goddess: Rebecca Apsan

Time Inc Digital Studios

Bonus! Apsan shares some of her all-time favorite flirty lingerie pieces:

1. Silk camisole ($150) and boxer shorty ($125), La Petite Coquette; thelittleflirt.com.

2. Lace bra, Chantelle, $78; chantelle.com.

3. Lace and mesh bra, Timpa, $36; journelle.com.

For more pros’ tips, tricks, and best-kept secrets, pick up a copy of InStyle’s July issue, on sale and available for digital download now.

In need of more fashion inspiration? Find out how you can wear pajamas in public in our gallery!