I spent more than a decade as editor of a publication which featured cruise travel, so I've heard great insights from officers, the captain, travel agents and other travelers. One of the best I've heard is: Avoid the white space!
It's what you DON'T see in those glossy brochures and Web site layouts of the ship's decks that should be of concern as it will affect how much rest you will be able to get aboard ship, how much access you'll have to amenities, etc. Sadly, I learned the hard way.
Then an officer explained to me: "Avoid the white space." What that means is that because of security reasons, the layouts you see cannot list the location of common areas such as stairwells or even some group gathering spots.
What does that mean? You may be spending extra money and getting no return. I wanted a mini-suite for the extra room once. You would assume because you are paying more and getting more room, it would mean more comfortable accommodations. Take a close look at that layout, noting the dreaded white space, and you may find out that your room is located directly next to a main stairwell or below the basketball or shuffleboard area.
It isn't about picking out the right cabin, necessarily. It's about carefully seeing what is around you and knowing yourself well enough to know when it's worth the money to get the extra stuff.
If you are ready to book a cabin and you see white space above you or to the side of you, ask a travel agent or a representative of the cruise line. Your extra dollars on the cabin could be better spent on more photos, an extra excursion or the like.
It only takes a single episode of almost not making it to the port on time -- or missing the ship altogether! -- to make getting in town the day before... very much worth it. 
