From Marco Polo airport, you can catch the regular bus service to Piazzale Roma - it takes 20 minutes. Then take the vaporetto (water bus) number 2 in the direction of Accademia- San Marco on the Grand Canal - it takes 20 minutes .
Get off at San Samuele. It is 150 meters on foot. You can also take the vaporetto number 1 in the direction of Rialto-San Marco. Get off at Sant'Angelo - it takes 25 minutes. If you get off at Sant'Angelo, follow the signs to Palazzo Grassi.

From the railway station to San Samuele:

From the railway station, follow the same directions as from Piazzale Roma.