The Prague Information Service (PIS) is centrally located and has information about concerts, performances, and other happenings in the city. They have maps and publish a monthly guide for tourists. The staff is very knowledgeable and English-speaking.

Prague Information Service
Straromestske Namesti 1(Old Town Hall)
Rytirska 31
Main Railway Station (lobby )
Lesser Town Bridge Tower (summer season)

This is the Czech Tourism official site with lots of information about Prague. You can also email PIS in advance with queries or help planning your visit via website above or using Answers (in English) very comprehensive and prompt; you should receive a full reply in a only a couple of hours!