Cruising is a great vacation if you do the homework, and ask the right questions of your travel agent. Big questions that you want to make sure and ask are as follows:
That they have a disabled accessible cabin available. These cabins are larger and have the grab bars, and shower bench. Plus it offers a clear path for a wheelchair or walker.
Does the ship dock, or do you have to take a boat to get to the port? It is important because the cruise line will not assist you onto the tender. If you will be upset if you don't get to disembark at each port, then you will need to really get an answer to this. Are there any accessible excursions? You must realize that most of the ports you will be visiting are in developing nations and are not bound by the ADA. If you are pretty active and can get into a full size van you should be OK, otherwise you might want to go with some people who can You HAVE to have a passport. They will not let you on board if you don't have one (you may be able to get a passport card but you need something to prove your citizenship). If you show up without one they will forfeit your payment and you will be out of luck.
lift you in and fold your walker/wheelchair/or other mobility vehicle. 
Is this a REALLY a kid friendly ship? You don't want to take a trip if the kids in your group won't have any fun. Again do your research.
Bring scope patches even if you don't think you will get sea sick. You just cannot tell how you will respond on a different cruise. It will save you in the end if you have it (better safe than sorry).
Cushion your trip with a day on both ends for jet lag. Several hours of time difference can really affect you and possibly wreck your trip.
If you can take short cruises, do so. It gives you a chance to relax without costing a fortune and you can book longer cruises on the ship and get a discount.
Be prepared to roll around like Jack Sparrow. I was in the eastern Caribbean and could not roll a straight line if I tried. You are on a ship and everything moves. Just get used to it.
There is something about taking a cruise that puts you back in touch with yourself. It is a primitive experience that has you out literally in the middle of nowhere. Today's cruises are luxurious by past standards but are part of a link from our past. Every civilization had at least one person that said "I am hopping in that boat and going to see what I can find". More later.
