If you are sure that you're staying at Venice and not mestre, the easiest way is to take the bus, it takes about 20 minutes. I was backpacking there, and I stayed half a block away from Santa Lucia rail station. I recommend you from the bus stop to walk to your hotel, it takes about 3 blocks, and you get to "experience" Venice with the canals and bridges from the very begining. Lovely!
Venice is small enough to walk it entirely, and the vaporetto is the best way to get to the other islands: Murano, Burano, the Cementery, etc.
Good luck in such a lovely city! if you want a gondola ride, bargain a lot!
Regards )( Arcano
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