There are countless places to visit in Venice, but it may depend on what time of the year you were to come. Venice is similar to Florence weather. It is hot and muggy in the June and July period and cooler in September, although Venice is slightly cooler than Florence in the Autumn period, especially in the evenings and rains quite a lot during this time. To add to this the high tide will come in, known as the aqua alta which can be quite an experience, but something you would probably want to avoid.
The aqua alta can leave you walking over planks to avoid stepping in water. The alternative is wearing boots and treading in the puddles in the city, which many of the tourists actually enjoy doing.
Winter in Venice can also be an experience and maybe even more romantic. There are many bars around to keep you warm where you will be able to sip on espressos and hot chocolate. Make sure you bring extra clothing with you if you come during this time. Sometimes you will be able to see snow near the canals. Hotels will be cheaper at this time because this is the quiet season and there will be less tourists in town so you will be able to mingle with the locals.
In February the accommodation rates rise as the carnival comes to town. It will still be cold, but the atmosphere is good with people wearing the local masks you will see displayed in shop windows and dressing up appropriately. September has a film festival and the prices of hotels will once again rise.
If you decide to visit Venice during the heat of Summer stop by at Lido, where you will be able to find some of the best beaches to cool you down. The sunshine will hit the town from May and will really heat up during June and July. August is the time when the locals will take their vacation. Most of the locals close their shops or restaurants so you may be annoyed to find a lot of things closed and this might not be a good time to come to Venice. Different people will have different ideas when to visit Venice , depending on what they enjoy doing and their style of travel. It is up to you to plan your trip around what is happening and the weather you prefer to travel in.