The easiest way to to take a land taxi to the port if the ship is docking at Marittima or San Basilio.
A good site for info
It is a good idea to arrive a day ahead in case of flight/weather delays.
You can check which pier your ship will dock at
Alexandr Pushkin, Carnival-Holiday, HAL-(old)Westerdam, Orient lines-Marco Polo, Royal Olympic-Olympic, NCL-Dream, Dawn-Princess, ACCL-Grande Caribe, Oceania-Insignia (3), Regatta(4) Marina (1) St Lawrence Cruise Lines-Canadian Empress
Scenic River cruise June 11,2012