You can visit Venice at any time of the year, and the city will welcome you with its beauty, although the months of high summer from June - August, can get very hot, and the streets get crowded with tourists, making it quite frustrating to get around.
From March - May and September - October offer the best of the weather, and a trip during these times will be very pleasant and less busy.
November is the time of year best avoided, as the city regularly floods, and you can find yourself ankle deep in questionable looking water.
Visiting during the highest seasons of Christmas, Easter, and Carnivale is great, although high demand for accommodation at these times mean that rates are much more expensive.
