Wash your hair with a highlight enhancing shampoo. Work a bit of volumizing mousse through your roots so you get extra lift without working too hard.
Quickly blow-dry on a medium heat (don't worry about getting every strand perfectly smooth, you can tame flyaways with a little anti frizz serum later.)
Make a deep side part and pull hair loosely back from either side of the part, fastening hair with a tiny claw clip. This way you'll have that tousled, loose effect but your hair will still hold where you clip it.