I think the most obvious question to break the ice is to ask where are you from, seems like a good place to start...Then you can get into their cruising history, always works for me.
That works for me as well.
Carnival Liberty New Year's Eve 2007
Liberty of the Seas 5/2008+11/2009
Allure 1/16/ 2011
Independence of the Seas 12/29/2013 Top-notch!
I usually ask where people are from . On a cruise last year a couple was seated next to my wife and I in the buffet area .
As it turned out the husband and I grew up in the same area at virtually the same time .
not like we are cruise experts or something but when on the first cruise last year the first night we went to the dinning room and were sat at a 2 person table, a few minutes later another couple was sat next to us...so I of course being the out going type leaned over and said hello, where are you all from? we became friends and hung out the entire cruise....so I guess the "where you from" works good
Our first Cruise: Carnival Conquest 9/16/12 to 9/23/12
On another cruise we were seated at a table next to a couple and I asked where they were from .She replied that they live in Alabama ,I jokingly said you appear to have a NY accent and indeed that was where she grew up.