What a fantastic holidays! Venice is a fantastic city!
Venice carnival tips: Take with you a map of Venice, find a good map with a 1:5000 scale, like these one.
With a good map you'll be able to: 1) don't get lost 2) take the needed shortcut to stay away from the hordes of tourist 3) see and shot many interesting place with few tourists, they all go to S.Marco square :-)