Amen to everything Tweety said! In addition, pack, repack, and recheck luggage. Make a to-do and to-take list while you're fairly calm. This is especially important if it's your first cruise. Don't be surprised if you feel a bit dizzy while packing. That's just your cruise becoming real.
Also know that you will forget something. Keep your docs and passport in the same place. Check them daily. Make it a habit so you won't forget them in the last minute excitement before leaving the house. That has been my paranoia for the cruises I've been on.