WARNING! This is the key to book the cheapest flights possible to anywhere

1:}Book six weeks in advance. Passengers pay the lowest price, nearly 6 percent below the average fare, if they buy six weeks before their flight, according to a study by the Airlines Reporting Corporation (ARC).

2:} After compiling data from every U.S. travel agency over the last four years, it determined that most people booked the cheapest airline tickets 42 days in advance. But the six-week rule isn't necessarily a surefire strategy for snagging the cheapest fare. "This is just a trend," explains Chuck Thackston, ARC's managing director of data and analytics. "Airlines will make valuable deals available all the time. But, on average, we see this 42-day approach works."

3:} Scan for morning deals. Airlines only post a limited number of seats at a reduced fare at night, so Thackston advises snagging seats early. "Those tickets may sell out later in the day," he says. The early morning is the time you'll see most of these deals available, although a few airlines release discounted tickets throughout the day.

4:}Best time to buy: Tuesdays at 3 p.m. Eastern. If you don't find the discounts you're looking for in the early morning, a study by Farecompare.com says the best time to buy airline tickets and shop for travel (domestically) is on Tuesday at 3 p.m. Eastern. However, George Hobia, founder of AirfareWatchdog.com, argues that the best deals vary frequently, so there's not one specific day or time of the week to buy.

5:}Cheapest day to fly: Wednesday. According to a recent Farecompare.com study, the cheapest day to fly is Wednesday for domestic travel. "The day with the most seats is likely to have better supply, and thus ... more empty seats that require discounting to fill the plane—meaning they have to release more seats at their cheapest price point," according to the website. Other low-cost days to fly are Tuesday and Saturday, says Farecompare (Friday and Sunday are the most expensive days to travel).

6:}Fly out early. The cheapest flight is typically the first flight of the morning. "Yes, that means you have to get up at 4 a.m.," says Rick Seaney, chief executive of Farecompare.com. The next-cheapest flight times are during or after lunch or at the dinner hour. "Of course, the absolute cheapest time to fly is on those limited routes with red-eyes," he says.

7:}Check low-cost airlines individually. Comparison sites like kayak.com don't necessarily do all the work for you. Some low-cost airlines, like Southwest in the United States and Ryanair in Europe, don't allow their tickets to be quoted on popular comparison websites, says Seaney. So be sure to check them separately. And do your homework to make sure the so-called "low cost" airline doesn't tack on extra fees that drive up the cost, like a bloated baggage-check charge, which Seaney says is a tactic employed by some of the budget airlines.

8:}Sign up for free alerts on AirfareWatchdog.com. Almost every major online booking site offers airfare alerts that ping you when fare prices fall. AirfareWatchdog.com stands out from the pack by using people to vet deals rather than computer systems. "We only send updates when we think we've found a good deal, whereas other sites might update you when a flight drops $2," says founder George Hobia.

9:}Build a relationship. "The question isn't how much is it to fly from here to there, the question is, 'Who's asking?'" Brancatelli says. If you're an elite member of the airline's frequent-flyer program or if you have a credit card that's tied to the airline, you automatically have a leg-up on other travelers. "The more the airline knows you, the more it tailors its pricing to you," Brancatelli explains. Credit cards tied to the airlines now offer perks that were once standard, such as free checked bags, priority boarding, and seat selection, so they may be worth signing up for if you fly frequently on one airline.