I usually start by using the guidelines in the brochure from RCCL to tip the staff onboard:
bus driver (air to port, port to air/booked through RCI) Depending on how much luggage, usually $2.00 per piece.
luggage handler at port, Same as bus driver, $2.00 per piece of luggage.
room steward, $3.50 perday, per person
maitre'd, If he actually does something for us, and comes around everynite, $10.00
head waiter, same as Maitre'd
waiter, $3.50 perday, per person
bus boy, $2.00 perday, per person
snorkel excursion (booked through RCI)
glass botum boat excursion (booked through RCI)
some other tour excursion (booked through RCI)
With the people running the excursions, usually a few dollars, sometimes the bus driver will narriate and crack jokes, another few dollars.
That should cover it, enjoy your cruise!