Here is some practical advice from an experienced Cruiser.
1.
Decide the length of the cruise you want to take - there are 7 to 16 days cruises available.
If you are a first time cruiser - check if you have sea legs and stomach.
For this take a short boat ride or be on water for a while.
There are medications which sedate the person but nothing wrong in checking your seaworthiness.
2.
If you are travelling from a different continent or time zone, it is advisable to take stay in a hotel in the home country for a few days to acclimatize and let your body adjust to the change in the time zone and let the jetlag wear off.
You will be more grounded and be able to enjoy your cruising experience.
3.
The peak season for European Cruises is August though the season begins in April and lasts through to October.
Also keep track of the weather - the temperatures can reach as high as 45 degrees in Mediterranean.
4.
If you are an experienced cruiser then you will choose the cruise to experience different ships and if a first time cruiser you will choose the cruise for the itinerary.
This is because the primary excitement is about the places you will be able to visit - which was the primary goal.
The next time yes the magic of the city calls you but also does the intrigue of experiencing different ships and what they have to offer.
This will help you choose your ship.