Know when to book early and when to wait for a better price.
It's the million-dollar question: Should you buy now or wait because the price could drop? The more unusual the itinerary and the shorter the travel window—say, a cruise to Russia and the Baltic, where the good weather lasts only about eight weeks—the more likely the voyage will sell out quickly and, therefore, the more important it is to book early. For an itinerary that is repeated for months on end, however—as in the Caribbean—it's wise to wait (unless you need a specific type of cabin that could sell out). Generally speaking, for the mass-market lines, which have been steadily lowering rates as the cruise date approaches, you're better off waiting to book, says Mary Jean Tully, CEO of The Cruise Professionals in Toronto and a top producer for many cruise lines. On the luxury lines, however, strategies vary from company to company. A traveler should have no qualms about booking a Crystal Cruises sailing early because, if the fare drops after you pay, the line promises a refund of the price difference. And the best travel agents—true cruise specialists—offer their clients a "best price guarantee" on every cruise they book, which means that, should the cruise line drop its price, they will protect their clients, even if they have to make up the difference out of their own pockets.

Obtain an official cruise line invoice showing the total upfront cost of the cruise that interests you, without putting down a deposit first.
You can do this if you're using the right travel agent. Say you're intrigued by Oceania Cruises' offer of free airfare and two-for-one cruise fares in Europe. The advertised price for a 14-day cruise from Istanbul to Venice in a penthouse suite is $7,499 per person. Yet the total for two on the invoice is a whopping $18,870. Why? First of all, the "free airfare" actually costs $1,018 in air-related taxes, fuel surcharges, and ticketing fees. Government fees, taxes, and security and handling charges total $728. Airport-to-ship and ship-to-airport transfers add on $344; insurance, $1,684; and Turkish visas, $98. That's how you reach $18,870.

When there's an offer of "free airfare," be sure to get the price of the cruise both with and without the airfare.
The cruise-only price can be hundreds of dollars less than the cruise-plus-free-airfare price. Example: A deluxe suite on a 13-night Baltic and Russia cruise on Regent Seven Seas is $19,180 without the free airfare but $21,480 with it. "When they give you free airfare," says Turen, "they inflate the cruise price to cover most of the cost of what they're giving you for free."

If you're choosing between different cruises, calculate the cost per day of each.
It's the only way to do an accurate price comparison, Turen explains. Follow this mathematical formula: Take the total price of the cruise as shown on the invoice, subtract any airfare, air-related taxes and fuel surcharges, and travel insurance, and then divide that number by the number of cruise nights. Here, for instance, is how to compare the costs of two different European cruises in September: (1) A seven-night cruise from Athens to Istanbul on Regent Seven Seas' Navigator in a minimum-category outside cabin (301 square feet, no balcony), priced at $3,805. (2) A 12-night sailing from Istanbul to Venice on Crystal Cruises' Crystal Serenity, also in a minimum-category, non-obstructed-view cabin (226 square feet, no balcony), priced at $5,480. The cost per person per day is $543 for the Regent Seven Seas cruise, $457 for the Crystal cruise. The Crystal cruise costs $86 less per day. It doesn't include the shore excursions, gratuities, and alcohol that the Regent cruise includes but, considering that it's on the ship that Condé Nast Traveler readers rate number one (the Serenity scores 93.3 in our 2009 Cruise Poll, the Navigator 88.1) it probably represents better value for one's dollar.