From Marco Polo Airport you can take the Alilaguna Water Bus, either the Blue Line or the Orange Line. For the Blue Line, you would get off at the Fondamenta Nuove terminal. From the terminal, it's perhaps a 10 to 12-minute walk. If taking the Orange Line, you would get off at the Rialto terminal. From here it's about the same distance to your hotel. The Alilaguna Water Bus crosses the lagoon going out to Venice so it can be a great way to approach Venice if the weather is good.
Another option would be to take a bus or taxi from the airport to Piazzale Roma. From here you would take the Vaporetto, line 1 or 2, and get off at the Rialto terminal. The Vaporetto is the public water transportation system in Venice.
I would advise you to get specific walking directions from your hotel from both terminals as it is easy to get lost in Venice. The last option would be to take a private or shared water taxi. The benefit with this service is that they will take you to as close to your hotel as possible as their smaller boats can navigate the canals that the large boats can't This service will be the most expensive option.