Remember that tips are already included in the flat fee that goes towards a central fund for the staff, so there is no need to tip separately!
Be courteous. When you are polite and friendly with the crew, you'll find that they are far more willing to help you out than if you are always snapping orders at them. Be nice and they'll be nice right back.
Take the time to thank people. While on a cruise, you should still keep your manners about you and thank everyone who does something for you . . . even if they are being paid to do so. A simple thanks can go a long way.
Criticize everything. Yes, you paid good money to go on this cruise, but hopefully you did enough research to know what to expect. Relax and enjoy the cruise, rather than looking at the bad side of things.
Become a cruise stalker. While you are bound to make new friends on the cruise, it's one thing to get together in the hot tub or for drinks, quite another to follow them around the ship all day! It's a good idea to befriend several people so you have a variety of friends to hang out with.
Complain to random crew members. If you have a complaint, you should go through the proper channels and not just pick someone at random who probably has no idea what you are talking about and can't possibly help you. Instead, speak to the manager of the area you are having issues with. For example, if your problem is with the waiter, speak to the head waiter.
Slam your cabin door. Taking a moment to close it quietly, particularly at night, will help keep the peace among your neighbors! The same goes for talking loudly in the corridor . . . it can really be obnoxious to fellow passengers.