Your hotel is located between Campo San Giovanni e Paola and Campo Santa Maria Formosa. I think the “best”way for you, meaning the best combination of low price and simplicity, is to follow the very clear directions on the hotel website. They suggest using the the Alilaguna.
https://www.foresteriavenezia.it/accommodations-castello-quarter-venice/
The Alilaguna is a water bus that goes across the lagoon directly to various docks on the island of Venice. There is a clear walkway from the airport arrivals area down to the Alilaguna dock. Buy your tickets before boarding the boat, and get off at Fondamente Nova. The walking directions from there to the hotel are very good, using landmarks.
They also describe the route to the hotel by taking the vaporetto from Piazzale Roma to Rialto and walking from there. This is more complicated, because you have to first take a bus from the airport to Piazzale Roma, then board the right vaporetto going in the right direction, and then navigate on foot a more complicated route from Rialto to the hotel.
The third way, which they do not mention, is to take a water taxi directly from the airport docks to the dock nearest the hotel. The water taxis can go into the small back canals and get you quite close to your hotel. But this is far more expensive than the other methods—-over £120 for a private water taxi; slightly less if you take a shared one.
Here are good directions for walking to the Alilaguna boat dock from the airport arrivals area. Note that you buy your tickets for the Alilaguna before exiting the airport arrivals area.
https://europeforvisitors.com/venice/articles/venice-marco-polo-airport-moving-sidewalk-to-boats.htm