I've been on numerous cruises.  The first dozen or so were on big grey ships that offered free "food" and a nice bunk to sleep in.  The price was right though and I got to see a lot of interesting places.

 

Regarding the cruise you are talking about, I've been on a few of those as well.  From my experience, a 3 day cruise is too short and a 7 day cruise is just a bit too long.  A 5 day cruise is just about right.

 

My advice is to go to the shows, especially the "after hours" or "adult" shows for some great entertainment if you are not offended by vulgar language.  What my wife and I did was get a few simple "Thank You" cards and put a generous tip in them.  At the end of the cruise we would hand them out to the various people that waited on us, especially the people that took care of our room.

 

I do recommend splurging a bit for a room with a balcony.

 

The most expensive part is going to be drinking, gambling in the Casino(s) and any shopping/souvenirs that you might purchase.  The excursions that are offered are pretty good, or depending on which port you pull into, it's worth hiring a taxi driver to show you around.  I wouldn't really recommend the latter if it's your first time in a foreign country, but sometimes you see more and do more taking this route.

 

The bottom line is to relax and enjoy yourself.

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