I really like seeing girls dressed like this (how hermione is dressed of course):
link of course, emma watson is smoking, so this might not work for every girl, but in general I think its a really good look on just about any girl.
if its too hot for jacket, a nice t-shirt that has short sleeves and is kinda tight/fitted, or a wife beater type top can look hot.
obviously short shorts are hot if the girl has nice legs...I am only a man after all...