Holiday travel tips: Save on cruises for a holiday at sea, plus when to book Thanksgiving airfare

Put the sea in the holiday season this year with expert tips to set sail with the best cruise deals on deck, plus advice on timing to score savings on airfare for Thanksgiving.

Brian Kelly, founder of The Points Guy, joined "Good Morning America" on Friday equipped with his best holiday travel booking tips.

Tips to save when booking a cruise vacation

"Buying a cruise is like getting fashion. If you want the shiniest, best new ship you're going to pay top dollar," Kelly said.

Book a cruise 90 days out

"At 90 days prior to sailing, the cruise lines really start discounting cruises. So that's the 90 day mark where you want to see what discounts are being offered, and they can be substantial," he explained.

Kelly suggests looking at travel planning websites like Vacations To Go, which has a 90-days-out tracker that shows all the available cabins.

"You may not have your best pick, but the deals can be substantial," he said. "And we're about 90 days before the Christmas and year-end holidays, so now could be the time to start looking."

Best luxury cruise deals: Transatlantic crossings

"Part of doing a luxury cruise is just staying on the ship. Most cruise ships, you can get entry level cabins around $1,000. Luxury lines, you're talking $4,000 and up," Kelly started. "But here's a special tip: Between October and November, [some of] those luxury cruise ships go from the Mediterranean to the Caribbean."

"So you can tack on a transatlantic crossing, which may not sound luxurious, but when you're on one of these fancy ships where the ship is the destination, you can get a 13-day crossing including a week in the Caribbean for less than what [the price of] one week in Europe would be."

Last minute cruise deals under $100 per day

While selection may be limited for last-minute planners, Kelly said, "There are deals where you can spend less than $100 a day to go cruising in the Caribbean."

"I highly recommend going through a travel agent if you're booking cruises," he said, adding, "Choose the two that have the best [offer] and then have them negotiate against each other for extra perks, upgrades and things like that."

Kelly suggests using a virtual service such as Cruise Compete that does that step for you once you select where and when you want to travel.

Where to book low airfare for the holidays

Kelly and other travel experts often refer to the timeframe of booking the best airfare as "the Goldilocks window," which is booking at least 60 days in advance for international and about 45 days out for domestic.

Book Thanksgiving six weeks in advance

"For that Thanksgiving travel, luckily this week and next week in general are the best," Kelly said on Friday. "It's about six weeks prior to the date, and Thanksgiving is a little later this year, so you're not out of time."

Kelly added, "If the price looks good on Google flights -- it will tell you low, medium, high -- if you are seeing anything in that medium or low [range], take it. Even if it's high, what you can do, if the airline does end up dropping the price, [is] track it -- and you can get a voucher back."

If the price drops enough, even a small amount, Kelly said, "You can get a voucher in your account for the difference in what the price dropped" by going online and rebooking directly through the airline.

Golden rule for booking flights: Advanced purchase requirement

Fellow travel expert Scott Keyes of Going.com, formerly Scott's Cheap Flights, regularly reminds people to follow this golden rule of air travel: back-timing when to book based on your departure date, in order to align with an airline's "advanced purchase requirement" found in the fine print of the fare terms and conditions.

"Pull up a calendar and circle 21 days before your travel date," he said. "That needs to be your sort of drop-dead date to get your flights booked by."