Eating well in Venice requires some effort and some navigation. The city's tourist economy has produced a large number of restaurants serving mediocre food at high prices to visitors who won't return. The good restaurants — and there are excellent ones — tend to be slightly off the main routes and rely on reputation rather than foot traffic.
Venetian cooking is built around the lagoon and the Adriatic: fish, shellfish, cuttlefish, lagoon crabs, and the tiny grey shrimp (schie) that are eaten whole. The cucina veneziana also draws on centuries of trade with the East — sarde in saor (sweet-sour sardines with onions, raisins, and pine nuts), risi e bisi (rice with peas), and baccalà mantecato (whipped salt cod) all carry flavours you won't find elsewhere in Italy. Polenta replaces bread as the carbohydrate base in many traditional dishes.
The best neighbourhood for eating is Dorsoduro, particularly the streets around Campo Santa Margherita and the Fondamenta della Misericordia in Cannaregio. San Polo around the Rialto has the most concentrated bar and bacaro scene. Avoid restaurants that tout from the doorway or display photographs of food — a reliable indicator of quality.