1. Before your cruise, ask yourself how you want to spend your day in each port.
The best of the cruise lines' prefab group tours focus on adventure sports (climbing an Alaskan glacier), limited-capacity vehicles (a helicopter aerial tour), and activities that you could not do on your own (ziplining through the jungle). If your goal is to see cultural sites, however, you can visit less touristy spots by going without a group. Find out whether you can get to these places by taxi, rental car, train, bus, or ferry, and whether there will be enough time to return before the ship sails. Be warned: This is not always easy to do, and ships can switch piers at the last minute—which is why it's important to abide by tip No. 2.

2. Book through a cruise specialist.
Use a travel agent—such as those listed in "Top Travel Specialists"—who knows every inch of each port and can arrange for cars, drivers, and/or local guides who will customize a day tour. I asked cruise specialist Richard Turen (630-717-7777) to organize my Jost Van Dyke excursion, because I found it impossible to do so on my own: None of the boat operators I contacted were willing to take me there at an affordable price. Turen also recommended eating at La Samanna and hiring a car through Ladera Resort. Excursions booked by travel agents are usually less costly than the ship's tours if your party consists of three or more people. Example: Our car and driver from Ladera Resort cost $160. The St. Lucia bus tour most similar to ours (minus the highlight: the cassava bread factory) cost $116 for two.

3. Book ship-arranged tours in advance.
High-demand shore excursions sell out fast, so sign up early even if you're not sure. You can usually cancel and get a refund up to 36 hours in advance. Shore excursions on large-ship cruises can typically be booked online months ahead of the sailing date. Small-ship cruise lines furnish descriptions of excursions, but you usually can't book until you're on board: Sign up fast.

4. Call ahead to a local concierge if you want to visit a hotel.
Perhaps you'd like to eat lunch or play golf at a nearby resort. Some concierges will arrange for a car and driver to pick you up at the pier and show you sights en route; you'll end up with a much better guide than if you hailed a random taxi.

5. Research local events and festivals.
Is there a sports tournament or a cultural festival going on? Check out sites like whatsonwhen.com. If your ship stays late, you might have time for the theater or other entertainment. If you're overnighting in Sydney, for instance, get tickets to the Sydney Opera House.

6. Contact a local tour operator.
Say the activities that interest you are not offered by the cruise line. Go to the tourist board's Web site and find a local agency that can arrange what you want. In Jamaica earlier this year, I met a family at the Rocklands Bird Sanctuary who were on a cruise but, through a local tour agency, had hired a private van to take them white-water rafting and then to the bird sanctuary. They were delighted with their day.