Venice

There will be land buses, cabs and trams to a square called Piazzale Roma, the "gate" to the floating district of central Venice. From there you can walk to Piazza S. Marco, take a water bus or get on an expensive water cab.

They work like their wheeled counterparts, with the relevant exception that you need either a bridge or a water bus to cross the street in Venice!

Staying out of Venice you'll see it like a day-tripper, without the benefits of day-tripping. Imho.

Dario is correct, by not staying in the city, you miss the beauty of the first light on the canals and the last echos of people (you) finding their way through the alleys on the way home at night.
Riding the Vaporetto's when there are no lines and only one or two (scraggly looking) passengers is a different experience than the one when the crush of the cruise boat crowd consumes every inch of the most popular places.
Venice comes alive in a different way when you can see it as a local might.
We like to stay in Dosodouro but there are probably other better options.

Once you take the bus into Piazzale Roma its a short walk to the vaporetto stop in front of the train station. It's also a nice walk to San Marco which takes 30-45 minutes. I'd try to do both so you can enjoy the scenery as each are very beautiful. Good luck!

shame you don't want to stay in Venice, but I'm sure you have very good reasons.

Once you get off the bus in P.le Roma you can ride a waterbus called vaporetto, or pay a lot for a water taxi, or walk...

The early mornings and from sunset on are pretty magical in Venice.

I don't know when you will be in Venice. This week the only long line I saw was for tickets to St Mark's Basilica. There were no lines for the vaporetto (water bus) at the most popular places - train station, Rialto and St Mark's (San Marco).