It's no accident that many cruise lines advertise their vessels as "floating hotels." Most mainstream ships offer U.S.-style accommodations, with tasteful (or sometimes not!) decor, televisions and room service. However, unless you can afford a suite, get used to the idea that your stateroom, or cabin, is not going to be palatial in size (think more in terms of about 150 sq.ft.). Some of the older ships, such as the Stella Solaris and the Enchanted Isle, have the largest staterooms (but not generally the most luxurious). If you want a sitting area or a balcony (the single most popular ship feature with cruisers today), you're going to pay more. However, if you're going on a long trip, or if you get claustrophobic, it's probably worth the extra money. Windows are replacing portholes in a big way on new ships, so be sure to ask your travel agent about that. (Also, if the view is important to you, make sure yours isn't partially or completely obstructed by lifeboats!)
Again, unless you're traveling on a newer ship or have a suite, queen-size beds are a rare commodity. On some ships, singles can be pushed together; on others, they're bolted to the floor. Some rooms have two beds on the floor and two bunks above that fold into the wall. Try to work out your sleeping arrangements in advance with your cruise consultant!
Shipboard features that always draw comedians' best lines are the very loud, pressurized toilets and the doorway ledges that require passengers to step up and over or else suffer the consequences (smashed toes!). Other little things you'll quickly become acclimated to include weighted chairs -- they're a little tougher to move around in the lounge!
One of the first things you'll need to learn in order to find your way around your ship is the proper use of the terms, starboard and port. Starboard refers to the right side of the ship (when you're facing forward); the port side is the left side of the ship. You'll also hear forward and aft, which refers to the front and back of the ship.
The public areas on ships -- show lounges, auditoriums, lecture halls -- are usually roomy and attractive. On most ships, there are plenty of little nooks and crannies where you can sit quietly and enjoy the view or read a book -- you just have to find them!