It's important to remember that there's no magic, secret, or guaranteed way to get an upgraded cabin. Like with hotels and airlines, it's often luck or being at the right place at the right time. However, there are a few things you can try to improve your chances of getting an upgrade.
Book the Cruise EarlyBooking a cruise early will sometimes result in an upgrade. Cruise ships usually sell out the most expensive cabins and suites first, but often the cheapest cabins come next. If you are one of the first to book a cheap cabin, you might get upgraded as the cruise date gets closer if demand is high for your cabin category.
Be a Frequent CruiserLike with airlines and hotels, cabin upgrades often go to members of the cruise line's frequent cruiser programs. If you are a frequent cruiser, you might also get free Internet access, free laundry, or other perks, depending on the number of days you have sailed with the cruise line.
Unfortunately, sometimes being a frequent cruiser can be a disadvantage. A cruise line might not upgrade someone who already loves sailing with them. See the next tip.
Be a First-Time CruiserSometimes, a cruise line will upgrade either new experienced cruisers or first-time cruisers in order to get them "hooked" on cruising with their cruise line. There are two scenarios. Let's say you have always sailed with Cruise Line A, but decide to try Cruise Line B. The new cruise line might give you an upgraded cabin in order to encourage you to sail with them again. The second scenario applies to first-time cruisers. A cruise line might upgrade someone who has never sailed on any cruise ship in order to improve their overall cruise experience.
Ask Your Travel AgentCheck with your travel agent at the time of booking and again throughout the time before your cruise. Some travel agencies purchase blocks of cabins, and your agent might upgrade you if a higher level cabin is left unsold. The travel agent might also know from past experience which cruise lines, cruise ships, and cruise itineraries are more likely to upgrade. It never hurts to ask!
Book a Guarantee CabinBooking a "guarantee" cabin means you are only reserving a particular category, not a specific cabin. The "guarantee" from the cruise line is that you will get the category you have reserved or a higher one. The disadvantage of a guarantee cabin is that you might not get the specific area of the ship you prefer (or even the specific deck). The advantage is that you will be more likely to get an upgrade than someone who has booked a specific cabin since the cruise line will not have to ask you before the upgrade.
Monitor Price on Cabin Before and After You BookJust because you've booked your cruise does not mean you should quit checking the advertised prices as the time gets closer to your sailing date. Many cruise lines and travel agencies offer "low price guarantees" to encourage cruise travelers to book early. With a low price guarantee, you will get a refund or a shipboard credit if the price falls below what you paid. These extra funds could be used to upgrade if a higher level was available.
For example, our family of four travelers once booked a 12-day cruise over a year in advance of sailing. When the price dropped $700 per person, I inquired of the travel agency and got a credit. That $2800 paid for all our shore excursions and onboard expenses. What a pleasant surprise!