Prague is one of the best preserved cities from the middle ages and thus a very beautiful place with lots of pubs, cafes, restaurants, cocktail bars plus very beautiful architecture. I will recomment the following a) Old town square and the street leading to the square, b) Charles Bridge, c) Prague Castle - walk there from Charles Bridge, d) Mala Strana area, e) Waclavske Namesti and Na Prikope business/shopping areas and f) go for a cozy walk up the top of Petin hill with nice view and very nice trip on a beautiful day.

Bars try Tretters,Bugsy's Bar, Bombay Cafe, Koziska, Soledni Nejstoda and Techtle Mechtle.
Disco try Mecca, Sasazu, aloha bar, Harleys, Infinity and phenomen.