I cruised on Norwegian Jade leaving from the beautiful port of Venice.
If arriving at San Lucia station you can use a porter service for €5 per bag which is worth it as it is difficult to get from the train to the ship with a suitcase. Once you have dropped your bag with the porters you will have to either walk to the port or catch the people mover then walk to the port. Or alternatively catch a taxi from Mestre station and you will be dropped at the ship this costs €35.
Embarking on to the ship is quite efficient and does not take to long and your luggage is delivered fairly quickly.