For some reason, my edit did not "take". Here is my revised post
From the common comments I see in first-time cruiser reviews, I'd offer the basic advice that they take the time to read the passenger contract carefully to make sure they understand what they are going to get... and not get... on their cruise. Following that, they need to go to the cruise line's website and read basic information of the FAQs, ship facts for the vessel on which they are sailing, and ports they are going to visit. Finally, go to their country's Department of State website and read up on country-specific issues and requirements to ensure they have the proper identification, permissions, and protections (e.g., passports, visas, vaccinations) to visit the countries on their itinerary.
These are basic training travel topics. Problem is there is a false sense of complacency where cruising is concerned. People don't seem to take the time to learn about what they are getting into. When problems arise, there seems to be a lot of shock and dismay along the line of "no one told me".