Gina Armstrong in O magazine

A recent family photo convinced 29-year-old Gina Armstrong, a resident in physical medicine and rehabilitation at Mount Sinai Medical Center in New York City, that she needed a foundation tutorial. "I noticed a clear line just below my hairline where my foundation ended," she says. "And my whole complexion looked sort of...yellow." So, after a 24-hour shift at the hospital, she headed to the O offices to meet with makeup artist Cynde Watson. Here's what she was doing wrong.
Applying foundation

Gina took a top-down approach to foundation application. "I started at my forehead and then worked all the way to my neck," she says. Her formula of choice: a cream-to-powder compact. "Not only was Gina using a foundation that's too light—which made her complexion look ashy—but she was applying way too much," says Cynde. "The purpose of foundation is to even out patchy areas—not change your entire skin tone."

See Watson's 6-step makeup makeover
pick the right shade of foundation

Step 1
Swipe several shades along the cheek to find the right color. "Choose the one that disappears into your skin," says Cynde, who recommends yellow-based shades for most women. (For Gina, she used Color by Cynde Watson Cover & Blend in Sun Brown, $18;
Prime skin with moisturizing gel

Prime the skin with an oil-free moisturizing gel or lotion (like Origins Starting Over, $45; It will help the foundation go on evenly and last longer.
How to dot foundation on your face

Dot the foundation on the forehead, chin, nose, and either side of the nose. Most discoloration is found in the middle of the face, so that's the only area that needs coverage. Use fingers to blend the foundation, gently pressing it into the skin.
How to blend concealer

Blend concealer over any darkness under the eyes, using a brush to get right up to the lashline and into the inner corners. The concealer should be one shade lighter than the foundation.
How to put on powder foundation

With a large, fluffy brush, dust a powder bronzer (like Shu Uemura Bronzing Powder in Dark, $38; around the perimeter of the face (hairline, temples, jawline). The shade should match these slightly darker areas, where the sun hits most.
How to put on sheer powder

If the T-zone tends to get shiny, brush a translucent powder (like L'Oréal Translucide Naturally Luminous Powder, $12; drugstores) over the nose, chin, and forehead.
Gina Armstrong in O magazine

The end result: perfectly blended foundation!

Next: How to Get Rid of Undereye Bags, Once and for All