I agree with the others in that you should get hooked up with a Travel Agent who specializes in cruises.
Some other things to consider are whether you would prefer a cruise that visits a lot of ports or spends a lot of time at sea. Port days can be very hectic and if you are on a 7 day cruise which visits 6 ports you may feel exhausted by the end of each day leaving little energy for nightlife.
If you enjoy meeting other people of varied backgrounds consider sitting for dinner at a table for 8 or 10. You're sure to find interesting conversation, and maybe somebody to pal around with on the ship.