I have decided not to visit Venice this year. At least not in this time of year when everything there goes crazy with the annual Carnival (Italians call it Carnevale di Venezia).
The best time to visit Venice depends on the purpose of visit. If you want to see the Venice Carnival with all the famous Venetian costumes, you obviously have to plan your visit when the event takes place. It starts around two weeks before Ash Wednesday and ends on Shrove Tuesday (Fat Tuesday or Mardi Gras), the day before Ash Wednesday.
That means in 2010 it takes place between February 6th and February 16th. If you decide to go these days, you have to be prepared to face hordes of other tourists from all over the world. Walking the streets of Venice during this period of time is limited to being carried along by a river of people. Obviously seeing most of the popular attractions during this time is literary impossible.
Also taking good photos is quite a challenge with all those crowds around.
If you choose some other time of year (for instance October or November), you will probably be able to avoid the large scale tourist pollution and have an opportunity to wander the narrow streets and enjoy the (at times smelly) canals almost by yourself. Actually you will never be all alone in Venice, but it can be quite nice even with some tourists around.
The drawback is that except inside many shops you won't be able to see any traditional Venetian costumes.
However there is a short period when you can taste a little bit of both. Just before the official Carneval starts, you can avoid the large crowds and also see some early costumes parading the streets. I am pretty sure they will be more than happy to pose for your camera. I would say the best time to do it is about two weeks before the official beginning.
That is roughly the period we chose last year. I shot loads of really nice photos and also had a great time. I strongly recommend it.
You can check out my photo results and read more about the trip by clicking on the Venice link under Labels somewhere in the right frame of this blog.
On the same link you will also find info on how the famous Venetian masks are made, how much such a day trip actually costed me, where to buy or rent a genuine Venetian costume and much, much more.
Also don't hesitate to ask any question on this topic. I'll be more then happy to help you out.