If you look at this link, What are gratuity guidelines for cruises? - Royal Caribbean International
, you can see what the recommended gratuity options are. Sorry, but I don't know how to insert a link with alternate text on this new forum.
The prepaid gratuities are done based on their recommended amounts, so it is done automatically, and they will give you vouchers to put in the envelopes that will be delivered to your stateroom on the last morning of the cruise. If you feel an employee has gone above and beyond what you expected, you can give additional cash in addition to the voucher. This happened to me a few years ago on my cruise on the Enchantment of the Seas. My dining room waiter, by the 3rd night, knew I wanted decaf coffee with whatever dessert I ordered. I did the prepaid gratuities, but also gave her a little something extra for remembering that.