Central Prague is very compact and walkable. If your hotel is in the Old Town, or almost anywhere in Prague 1, you can probably walk wherever you want to go. If you need transportation, Prague offers a multitude of options.
Metro: Prague’s metro is fast and reliable. There are several metro lines and all come thru the center of the city, with the main stops at Staremeska (Old Town) and Mustek (Wenceslas Square). It costs only 12 crowns per trip (about 40 Eurocents). There are discount cards for 3 or more days, but you are unlikely to need public transport that much to realize any savings.