For first timers, avoid the temptation to stay on the mainland or surrounding islands. The best time of day to see Venice is either early in the morning or late at night when the day trippers have gone and you have the streets to yourself.
If you're coming in the summer, then go for the Lido for a fantastic beach (for this part of the world) by day, then hop over to Venice for the evenings.
Also, probably the only city in the world where you shouldn’t bother reading restaurant reviews and recommendations before your trip. People get too emotional attached to "being in Venice" and even respected reviews from a source like The New York Times will be wildly inaccurate and ill-informed. I suggest just coming here and finding a price, location and venue to suit your situation.
Unless you plan on going no further than St. Marks Sq,
a good map is essential. This one online will help find any illusive bars or restaurants.
Nearly all hotels and restaurants are over-priced for the quality you will receive, and gondoliers will hustle you silly if you let them.
Oh, and Venice is sinking, but on the plus side, it means the thieving layabouts who work here will one day be out of a job. ‘Every cloud’ and that…