Here are The Traveling Professor's Top 5 Tips for Visiting Venice: 

Go in the Off-Season:  Venice is incredibly crowded, especially during the day due to the influx of cruise ships.  Try to avoid visiting in the summer months of June, July and August.  May and June is crowded too.  Prices are much more affordable in the off-season months.

Stay in the Dorsoduro section of Venice:  Areas near St. Mark's Square and the Rialto Bridge or generally overpriced and mobbed with tourists.  We find the Dorsudoro area to be close to the action, yet much quieter.   The restaurants tend to be more relaxing too.  The Traveling Professor's preference is the Hotel American Dinesen.   We like it because it is a top-notch 4-star, small, family run hotel.  It is located right on a canal so that a water taxi can pull right up.  No dragging luggage through (sometimes flooded) streets.

Get a Guide:  We found it well worth the cost to hire a guide for 3 hours to get us familiar with Venice.  It will cost about 65 euros and hour but they will allow you to skip the ultra-long lines at St. Mark's Basilica and the Doge's Palace.  The Traveling Professor can refer excellent guides.

Do as Much as Possible in the Evenings:  As mentioned, the huge cruise crowd packs the historic area of Venice during the day, making a visit to popular places like St. Mark's Square a hassle.  But go at night to enjoy the formal string orchestras competing across the square.   There is nothing like a moonlit walk in Venice.

Enjoy a Cichetti Crawl:  Frankly, I get tired of sitting at restaurants each and every night for dinner.   A good break is to go out for cichetti.  It's like a Venetian tapas.   The food is good, extremely authentic, and inexpensive.   Plus, it is a very social experience as travelers get the chance to meet Venetians and travelers alike in a relaxed setting.   Here is a good description of a cichetti itinerary.