Bring a credit card with a limit high enough to pay for an upgrade. Once you get on the ship, you will be using your credit card to pay for on-board charges. Make sure your credit limit can accommodate the upgrade as well as those expenses. If it won't and you still want to get a deal at the port, call the credit card company to ask for an increase or bring another credit card.
Arrive at the port as early as possible. Many people try to buy discounted upgrades at the port, so make sure you're at the head of the line. Take the earliest flight possible or arrive the night before your cruise and stay at a hotel near the port. Instead of using the cruise line's bus, which will put you in the middle of a crowd, book your own towncar or limousine.
When you enter the port, ask where you should go to look into an upgrade deal. Sometimes you can do this in the check-in line, but some cruise lines require you to go to the supervisor's desk. If you know this in advance, you can be getting a deal from the supervisor while others are waiting in the wrong line.
If there are no deals available, ask if something might open up later. If others bought upgrades ahead of you and they are being processed, their old staterooms might be available once the paperwork is done. If you are in a very low category, their rooms might be better than yours. It's possible to get a deal on one of them by asking later.
If you cannot get a deal at the port, ask whether anything is available after you board the ship. Once everyone is on board and the ship has left the port, you may discover that some guests canceled at the last minute or didn't show up. The purser may allow you to upgrade to one of their empty rooms at a cheap price.
