I have made several week long trips to Venice during the peak season of Carnevale Veneziano in February. If possible, try to avoid the weekends as it is too crowded to move, as you can see in the black and white photo below.
You have a better chance during the week, as there are less tourists, of meeting the local and international people dressed in traditional costumes. During their walks in various campi, campielli, the squares, open spaces of Venice. In addition to public events, parties and private masked balls are organized in the Venetian palaces, to relive the atmosphere of the past. If you prefer to see the local life of Venice go in the off-season.