I'm about to go to Venice for my 5th time next week. :-D This time next week I'll be on my usual wander. ;-) (You can see some of my Venice pics via the 500px link in my signature)
On my trips I take both my lenses, the 16-85mm and the 70-300mm. The 16-85mm is the perfect lens for me, and is used 95% of the time. The 70-300mm came in useful on my last trip when the Venice Marathon was happening, and on a previous visit when the Regatta was one too, but otherwise is hardly used. I'm determined to try and use it more next time. The alleyways are quite narrow, and wider is better. Even some of the open spaces are quite tight too. I always take my tripod, but only use it when it starts to get dark, and don't carry it around all day.
I've never been tempted to do any tours, because I'm always trying to do it as cheap as I can. ;-) It depends where the tour is going though, and if they can get you lots of popular views with some tips thrown in, then it may be worth it. Once you have a couple of good pics you'll not have the pressure of trying to get 'something'. I enjoy just walking around and getting lost, which is extremely easy to do. lol
Most tourists gather around St Mark's Square, and the Rialto Bridge, and the main route from the Train Station to St Mark's Square through the city is busy, and gets busier the closer you get to St Mark's Square. Burano is beautiful and very colourful, and although busy, most people stick to the central area where the shops are, and you can find some nice views wandering off the beaten track. Murano is nice, but eclipsed by Burano. If you plan on going to both, go to Murano first, as it could be a let down if visited after Burano. :-( ;-) Murano is good to see a glass making demonstration. Seeing a prancing horse made out of a blob of molten glass in a minute or two makes your jaw drop. Generally you find some things that you haven't seen before just by wandering about and getting lost in Venice.
Make sure you go up the Campanile's in St Mark's Square and San Giorgio Maggiore. I didn't until a couple of trips in, and wished I'd done it on the first trip. Lovely views over the city and the whole Lagoon.
And get yourself a travel pass too, they may be expensive, but when you find yourself emerging from the wrong side of the island with your feet aching, a nice gentle boat trip is a relief, and you may get some good views of the city, and other boats from on the water. Getting on at stop away from the more touristy places may get you a seat at the back or front too, rather than not getting a seat, or being stuck inside, especially on a trip along the Grand Canal.
Have a good trip.
