there is an excellent book about Mediterranean cruise ports, called Mediterranean by Cruise Ship
. I 've found that book to be extremely helpful in planning a Mediterranean cruise, as it not only features maps and shore excursion recommendations, but also lots of background information.
Princess uses Bacino Stazione Marittima, which is the main passenger terminal in Venice, which is less than once mile from Santa Lucia train station. There is a water taxi service from between the station and the terminal, and taxis run between Piazzale Roma at about half the distance to the passenger terminal. However, please note that those taxis are extremely
expensive (approx. 70-75 USD
Personally, if the cruise line provides some kind of transfer service from the station to the pier, I would definitely book it, as other way of transport in Venice are often either very expensive or inconvenient.