Depends on what type of cruising you want to do - we do not care for Carnival and definitely not Disney. My family is into the "old fashioned" dress up cruising, not the new relaxed, might as well stay at home, cruising. We have done several (4 Carib, 1 Mexico, 1 Alaska - NCL, Princess and Carnival.) We prefer Princess.
Other suggestion - don't book shore excursions ahead of time unless it is something you absolutely can't pass up! Don't fee as if you have to do ship activities at every port call. It is easy enough, usually, to get around the ports on your own, relax a little, and not spend quite so much money.
If your ship offers soda cards (I think they all do now,) and you are soda drinkers, buy one! Check to see if it covers juices. Some do, some don't.
Most cruise lines now cover your tips in your fare, make sure you find out. If not, and you leave tips, that will be a lot of extra money! Now, if you get exceptional service from someone, it would be nice to give a little extra, even if the normal tip is covered.
Have fun!!