If it's sunny, I recommend going to the beer gardens, there is Riegrovy Sady and Letenske Sady. Both overlook the city from different angles.
Pivovarsky klub (pivovarsky means brewery) has lots of beers and it's non-smoking. http://www.gastroinfo.cz/index.php?content=pivoklub Or there's http://www.gastroinfo.cz/index.php?content=pivodum which is more of a restaurant than pub.
Here you have your own beer tap on your table http://www.thepubworld.com/en/praha-1/
for clubs http://crossclub.cz for techno, jungle, dubstep
http://klub.roxy.cz roxy is always free on Mondays
http://karlovylazne.cz is the biggest club.. it's right on the oldest bridge, so you should find it.
enjoy the city