For round faces: Asymmetrical.
"A round face looks really good with an uneven cut, meaning a mix of lengths," says hairstylist and Los Angeles salon owner Chris McMillan. (Emma Stone's is a good example.) "If you add a deep side part and long, side-swept bangs, you'll look slimmer." Use a light finishing cream.
"If you want to wear a center part, the way to make it work for a round face is to have hair a few inches past your shoulders with layers that hit at the jaw," says McMillan. "Ask your stylist to cut in a bit on the sides to create subtle angles," as Kate Bosworth has. Prevent short layers from frizzing, which can add bulk around your face, by smoothing on a silicone serum.
An easy way to add definition is with a sleek ponytail secured at—or above—the height of your ears, says hairstylist and New York and D.C. salon owner Ted Gibson, like Fergie's here. The key? Keeping your hair smooth opposed to big and bouncy, which can add bulk. Gibson recommends running a light lotion.
The key to wearing hair above the shoulders is styling it imprecisely, says hairsylist Jimmy Paul: "Think of Renée Zellweger when she has a bob. It's a soft, layered cut worn intentionally mussed." Use a thickening spray.
Try a pixie like Ginnifer Goodwin's, suggests Paul. "All those little pieces help emphasize the cheekbones and eyes; it's almost as if you build in cheekbones with this cut." Apply a pomade.
"Try long, dramatic layers that sweep along the chin, and a shortening of the hair as you go back to the nape of the neck," says Paul. "This cut gives you structure and angles. The hard lines of it balance out the soft lines of a round face." Use a volumizing spray.
"If your face tends to look long, cutting straight bangs across the brow line can break up the length by creating the illusion of width," McMillan says. Keep them blunt like Taylor Swift's, with one or two passes of a flatiron.
"A center part on hair that's shoulder-length or longer is nice against an oval backdrop," says Gibson. To avoid looking too severe, add some soft waves, like Hilary Duff's, with a beach-hair-mimicking spray.
"A collarbone-grazing bob with side-swept bangs helps break up a long face and add softness," says McMillan. Carrie Underwood's fits the bill. Keep bangs in place with a pea-size drop of light gel.
"Though she has longer hair now, the iconic, edgy short cut Rihanna had is perfect for oval faces," says Paul. "It's definitely a 'notice me' look," he notes, so if you're feeling daring, go for it. "There's something very sexy and feminine about showing off your neck and ears with such hard lines." Use a medium-hold gel.
"A soft, tapered bob that hits right around the chin works beautifully on a square face," says Gibson. To add texture like Keira Knightley has and offset any severity at the jawline, mist on a dry shampoo spray.
Go for a shag with body, says Paul. Rachel McAdams's is a good example. Use a styling cream.
"Try waves from the ears down, which helps obscure any severity in the jawline," says McMillan. Megan Fox's is a great example of this look on long hair. Use a large round brush to smooth hair, then spritz on a wave spray .
"The way Demi Moore wears her hair—really straight and long—softens square angles," says McMillan. And the center part "opens up the middle of her face, drawing attention away from the jawline."
For a heart-shaped face, "hair that hits right below the jaw helps fill in the area around the chin, and de-emphasizes the triangle," explains Gibson. To blur those lines even more, add a bit of body, as Zoe Saldana has, with a round brush and volumizing spray.
With long hair, start with a clearly defined side part, then add side-swept bangs, suggests Gibson: "The idea is to bring your eyes out."
"You want a few pieces of hair to fall in the area between the ears and the nose to offset the width of the 'heart,' and you want the longer layers to fill in around the chin," McMillan says. And any waviness should be kept from the ears down, as it is on Jessica Biel here. "Fullness on top only emphasizes the point at the bottom," he explains.
"A pixie with soft side-swept bangs softens any hard features," says Paul. Carey Mulligan is a classic. Finger-comb a light cream before going over hair with a round brush and blow-dryer for smoothness.