Cruuising is a wonerful way to vacation. There are many things to keep in mind.
1- Budget- You probably will spend little time in your room. If you have a tight budget, take an inside cabin. Don;t go too low or too far back on the ship. Temper this with the kind of cruise. If you are cruising the caribbean, you'll pretty much see water from your cabin if you choose a window or balcony. On the other hand, an Alaska cruise has land, wildlife, and glaciers visible from your cabin most of the way. A balcony, if you can afford it, is very nice.
2- Crowds- you can book on a sail ship with just a few hundred people or on a mega ship with over 3000. Believe me, you can enjoy both and both have advantages and disadvantages. Large ships usually have more activities including entertainment like broadway shows etc. The smaller ships however have more intimate activities. If you cruising Alaska, the smaller ships have the ability to get into fiords that the large one can't.
3rd is itinerary- Alaska is my favorite but your chances of getting a tan, if that is important, are pretty slim. On the other hand, your chances of seeing a whale or a bear are pretty slim in Cancun.
Hope this helps.