Both Dorothy and Thomas so far are correct.
Let me give you an example.
I am MR. Cheap. I never book anything except inside cabins and hope for upgrades.
I almost away tip a ten or twenty to the waiter, busboy and cabin attendant on the second night of the cruise. I then proceed to jokingly say to the waiter how much I enjoy shrimp cocktail and explain to the busboy I love hot chocolate and water with no ice. I have more than once found a shrimp cocktail at my place setting quite a few nights.
Cabin attendants go out of their way to do extras when you reward them.
I also explain to the one I am giving to tip that I normally always give the regualr suggested tip at the end of the cruise and often more. The amount I am giving them now has nothing to do with my tip at the end of the cruise. All I am doing is letting them know I am on a vacation and want to have as good of a time as possible.
I can honestly say I have never been sorry I gave the extra tip in advance except once and that was when they changed busboy's on me. So I don't give the extra tip now until the second night.
As other posters have said, on other posts, with tips added to your account many staff will tell you their tips are less than before. I would guess, the reason, because most people believe their tipping respopnsibility is taking care of and it really is. But I want them, the service staff, to know I am determined to reward GOOD service above the normal tip. I also give an extra ten or twenty at then end of the cruise if the service was great.
I ALWAYs TRY TO FIND A PRIVATE PLACE WHERE I CAN GIVE THIS EXTRA TIP AND HAVE THIS CONVERSATION. I often will return to the dining room after we have left to do this.
I don't drink but if I did I would give the guy who hussles the drinks an extra tip also. I would almost assure you you would never lack a drink at least if he or she were arouind.
I will be on my 15th cruise in March and have used the above for 12 of the 14 previous and have found it works well for me. Hpe this helps.