How to get Ashley + Mary Kate Olsen`s "Messy" Hair look ?

I Love Love LOVE how the Olsen twins (Mary Kate + Ashley) sometimes have there hair the hole messy look but messy that works! I want to wear my hair like that next time i go out partyin can anyone tell me how to do it please Baring in mind that i wear clip in extensions so it would have to work with them thanks :)