Sailing on a luxury cruise means you'll be treated to excellent service, the best rooms and incredible dining. While you probably will pay more up front for a luxury cruise, pricing is often mostly inclusive -- you won't have to pay for those special extras, like Wi-Fi, fitness classes, gratuities and alcoholic beverages, onboard.

A number of cruise lines offer luxurious cruise experiences. Four of the most-inclusive luxury lines are Regent Seven Seas Cruises, Crystal Cruises, Silversea and Seabourn Cruises.

If you're looking to book a luxury cruise for couples, book when the kids are in school and avoid winter holidays and shorter summer sailings. September and October are ideal. Spring shoulder season, which peaks in May, also is a nice option for mild weather, depending on where the ship is sailing.

Luxury cruises are mostly inclusive, so you probably won't have to pay extra for things like alcohol, tips, Internet or even shore excursions. Ships tend to be smaller, and they can visit more intimate, uncrowded ports than bigger cruise ships. Service is intuitive, so staff onboard are trained to anticipate the needs of guests. You can also expect luxurious design elements, with marble or granite countertops, crystal chandeliers and curated art collections. Staterooms, or cabins, are often larger than you might find on other cruise ships. Many luxury ships are all-balcony or all-suite.

Luxury cruise ships are generally smaller than other cruise ships, ranging from fewer than 200 passengers to around 1,000. The best luxury cruises tend to have a favorable passenger-to-crew ratio; some have nearly one crew member for every passenger onboard. Luxury cruise ships also usually have a better passenger-to-space ratio, so ships feel less crowded.

Because luxury cruise ships are smaller than other cruise ships, they can visit destinations that are more unusual or off the beaten path. Luxury cruise itineraries are usually longer than other itineraries -- a weeklong cruise is considered "short" for a luxury ship. Expect to sail at least 10 days on a luxury ship. Many luxury cruise lines offer annual world cruises of 120 days or more. These cruises often circumnavigate the globe, visiting major cities as well as unique locations worldwide.

Pricing on luxury cruises varies depending on factors like the time of year you're sailing and the region you're visiting. Expect to pay anywhere from $300 per person per night to $600 or more per person per night. It might be tempting to wait for a deal on last-minute luxury cruises, but luxury lines generally offer the best pricing early on.