In case you are planning to go to Venice this year, the labiennale di Venezia starts 7 June and runs through 22 November. Some have asked about the Carnivale but if you can be in Venice during the International Art Exhibition, it would be well worth your time. There are art exhibits ALL OVER Venice. It's wonderful. You can choose not to purchase a ticket to go in the big art exhibit in the Arsenale area but it looks like there are some new additions. I believe the tickets for some of the exhibits were about 10 euro but it would have been well worth it. We just walked all over looking for art exhibits on the buildings and inside little alleys. You can go to labiennale.org to see what exhibits are being featured, or just Google biennale, Venice, Italy. We loved it. It happens every two years and this is the year!!
Be sure to have hotel reservations. Venice is packed at the beginning of the Biennale. I once arrived by train early in the morning expecting to find a hotel on the fly. I was able to find one from a runner waiting at the TI office in the train station. Later that afternoon I came back through the train station and there was a sign saying "Venice is full".