I assume this is the Norwegian Sun? She's a great ship, usually with a great crew, and I love her to bits.

MeLike2Travel's advice is very sound - take some time to navigate around the various different forums there, particularly those for the individual ports of call.

As a general rule, the ship's excursions are more expensive than those booked directly with the tour operators, usually somewhere between 50-100% more - this applies whether you book the ship's excursions before you go or after you get on board. However, there are some benefits with booking with the ship. First, you can usually cancel quite late without penalty if you change your plans, because you have direct access to the shorex desk on board; in contrast, communicating directly with a shore-based operator is more difficult when you're at sea or in a different country. Second, if you're on a ship's excursion and you're delayed, the ship will wait for you. You take on a certain level of risk in this respect if you go on your own - but then that applies even if you just walk to the shops and linger too long over your coffee. Third, the tour operators should be properly insured and meet the cruise line's standards - this safeguard doesn't always work but there are significant incentives for the local contractors to toe the line.

However, many people do book directly with local operators and skip the ship's excursions entirely. This involves a certain amount of legwork on your part before you go, but can save you money - and often get you better tours too.

If you want to go scuba diving and you want to book independently, make sure you do some thorough research. As your life literally depends on the integrity of the operator, make sure that they're properly approved and come with reliable recommendations. However, not being PADI certified won't stop you doing this; many PADI shops offer resort dives where you get a limited amount of necessary training before you do an easy dive. If you want to try this, you might even see if a local dive shop can do you a session in a local pool so it isn't all completely unfamiliar to you when you arrive at the port.

For ordinary tours, you have the additional option of just choosing when you get to the port. There are usually plenty of people hawking their wares at or near the quay when you arrive. However, you do take on a significant level of risk by doing this because you may have no idea who the operator is or what they really offer. If you're well travelled and used to judging people, this may be fine, but it would spook quite a lot of cruisers.

Don't forget to poke your head into Carlos and Charlie's in Cozumel, if they're up and running again by the time you get there and you have time. Always a good laugh, even better if it's busy.

And may I please indulge one pet peeve: She's a ship, not a "boat".

Have fun!