One signature look of Mary-Kate Olsen's casually bohemian style is hair that's not too prim or perfect -- which is why we love her laid-back hairline braid: Effortlessly cool yet pretty chic.

Get her look: Apply texturizer to hair, then randomly curl sections with a curling iron for subtle waves. Starting from behind one ear, loosely French-braid hair from the hairline area over to the other ear and bobby-pin in place.

The Olsen twins may sport the same basic layered cut, but just by styling differently you get two different looks. Mary-Kate (left) opts for messy waves while Ashley keeps her mane straight and simple. The twins are at Barnes & Noble in New York for the launch of their new coffee-table book "Influence", which details their fashion inspirations.

Create Mary-Kate's bedhead look: Blow-dry shampooed hair until it's 80% dry, then work in mousse. Twist hair up in a high bun and sleep in it overnight. In the morning, release hair and style as needed.