for a girl...definitely something colorful, if they can mix and match their colors well anything would look attractive
formal wear on a guy looks verrrrry good, especially black/white. but if a guy can wear a plain white t-shirt and plain blue jeans and STILL look good, then he'd look good in anything
a tee shirt with a dark colored blazer and some casual jeans...I wouldn't mind a leather jacket instead though. (for a guy)