Ignore my first answer. I accidentally posted it before I was finished.
Waiter - $3.50 per person per night
Asst. waiter - $2.00 per person per night
Room steward - $3.50 per person per night
This is what I've seen suggested as guidelines. Since most of these people's pay comes from tips, and since we've never had anything but excellent service, we tip more.
If you order room service, it's free, but I usually tip a couple of dollars.
Holland America automatically charges $10 per day per person on your charge account but the last time we went on Royal Caribbean they didn't do that.
Before we leave home, I usually prepare three envelopes with the suggested amounts in cash in them. As soon as we get to the room, we put them in the room safe. Then on the last day, we transfer the money into the envelopes they provide us and add more money if we want.
Hope this helps.