I am guessing most people do not think about doing this: plan two years in advance. To make sure I can get one of the best penthouse suites on Crystal Serenity and an early-bird rate (if there is one), I will know everything except the itinerary before the European cruises schedule for 2012 is published online. That way, the only delay is selecting the ports of call and I get lower prices than almost everyone else on board. So for me ship, then season, then itinerary will be the deciding factors. I will go in April or May so I can see the beautiful gardens, enjoy perfect weather, and avoid kids at the same time.