Potsdam is well served by trams and buses. Tram lines 91 and 94 run from the main station through the old town and out towards Sanssouci Park. The park itself is large — the walk from Schloss Sanssouci to the Neues Palais at the western end takes about thirty minutes — so comfortable shoes matter. Cycling is an excellent option: the paths through Sanssouci Park are well surfaced and the terrain is flat. Bike rental is available near the main station and in the Dutch Quarter.
For the Cecilienhof and Babelsberg Park on the eastern and northern sides of the city, bus lines connect from the main station. A day ticket for Potsdam's transit system covers all buses and trams and is worth buying if you plan to visit multiple sites.