TDouglas.. read through these topics and you will get many questions answered. For excursions, go to the Caribbean Port section.. you can find a lot of information there.
We loved St John's bay.. But there are so many choices. I guess my best advice would be to go to the "excursion seminars" they hold before you get to the first port of call. They will run through all the excursions and you can get a good idea of what you want to try from that.
As far as other advice goes, we kind of need a narrower topic to give you any real answers.
Carnival Cruise Lines:
Fantasy 90, Celebration 95, Victory 05, Conquest 05, Spirit 6/06, Freedom 6/08, Holiday 7/08, Victory 6/09, Valor 9/09, Dream 6/10, Splendor 8/10,Conquest 8/11,Magic 11/11,Triumph 4/12,Spirit 7/12,Freedom 11/12, Triumph 2/13 - The fire cruise
NCL Dream October 2006, RCCL Mariner OTS June 2007