when in Europe - I use Rick Steves as my reference (City and Country guidebooks). I Read about the country / city and decide what I want to see.
THEN I will see if I can do it on my own (Rick Steves Cruise Book, public transportation maps online, independent tours, etc), or if there's a ship tour that meets my needs.
But start by researching your ports and surrounding areas to determine what YOU want to do. And then work from there. And also take into consideration the "experts" advice. ie: Pisa for the Leaning Tower Of ... I've heard about it my entire life, "Had" to see it. Ignored the experts and went to Pisa (the Field of Miracles is pretty awesome) instead of going to Cinque Terre and boy howdy, do I wish we visited Cinque Terre or Siena instead.