RCI's tipping guidelines are:
Suite stateroom attendant: $5.75 a day per guest
Dining room waiter: $3.50 a day per guest
Stateroom attendant: $3.50 a day per guest
Assistant waiter: $2.00 a day per guest
Head Waiter: $.75 a day per guest
As Sonny says you will have the opportunity once onboard to have the gratuities put right on your onboard account. If you choose to do so, then you will receive coupons showing the gratuities were paid. You can put the coupons in an evelope to hand to the individuals so they know the gratuities were paid. You may add extra in the envelope.