There are several options for getting from the cruise terminal in Venice to where the main action is, Piazza San Marco, aka St. Marks Square. We found a site that outlines the possibilities from walking (most time, least money) to water taxis (most expensive) and combinations in between. The cruise line will provide transportation for any excursions booked through them, and they have an option of just transportation to and from St. Marks Square for $49 a piece, or we can get a 24-hour Vaporetto ticket for 18 Euro each. The Vaporetto is Venice's water bus system, and their routes take you all over the Venice waterways. We think we'll skip the gondola rides at about 80 euro per gondola, but we read that you can sometimes get a gondola to ferry you across the canal for 1 euro each, so we may look for that as a way to still get to experience a gondola.
Once we're out of the cruise terminal area, many of the sites that tourists are interested in can be reached on foot. We are planning to go over to Murano to see the glass makers on the first afternoon as part of a DCL sponsored excursion, but we have tickets to tour Doge's Palace and participate in their Secret Itinerary tour on the morning of our second day, so we have to figure out how to get there from the ship on our own.
We've had friends who have recently been to Venice share their tips for getting around, but if you have some to offer, please leave them in the comments!