To copy the coiffure, use a thickening spray before braiding (or you can even add extensions to increase bulk). Next, create a fishtail braid, and complete with a metallic ponytail topper, such as Free People's Stingray cuff ($18), or Elle's metallic square beads holder ($10), near the crown. Wear this braid during the day for a cool-girl look, or in the evening for a dressy, not-too-serious feel.
Blake Lively has a way with making any hairstyle all the more interesting. Take this thick, tousled fishtail braid, which she wore at the Savages premiere in New York. Instead of your average, off-to-the-side fishtail, Blake opted to break up the braid for an edgier, less-than-polished finish. She also played around with contrast, wearing a dressed-up, shimmery ponytail holder at its base, tying the bottom together by wrapping her matte-textured hair around the elastic.