Tipping is very simple on NCL. You will have a $12 pp service charge posted daily to you onboard account. No envelopes to stuff unless you are in a penthouse with a butler & concierge or use the kids crew
Tipping is back to a tip. You are not expected to give anthing extra to the cabin or wait staff. You can if you wish give someone a little extra if they go the extra mile. I often do that in the specialty dining venues.
Like every line 15% is added to bar tabs and a couple dollars for room service is the norm.
Without the service charge tipping the last night would be imposible since you may not have the same wait staff twice and the move from location to location depending on demand. The Great waiter you had in the Bistro last night may greet you in the buffet in the morning.
Questions ask away