You can scour websites and set up fare alerts, but the real secret in getting the best price for an airline ticket boils down to this: when you look and when you book.

Trouble is, not all peak travel times are created equal. The sweet spot when tickets are cheapest can vary by weeks, according to travel data analyzed by Expedia for The Associated Press.

Take the next two big travel weekends, for example. Based on an analysis of ticket prices over the last four years, Expedia has found that the best time to book for the Fourth of July was between one and two months in advance.

Jump ahead to Labor Day, in September, and the rules change dramatically. Those looking to travel that weekend, based on trends since 2007, can get the best deal buying three or four weeks in advance. Prices jump 10 percent from their lowest points if you wait one to two weeks out. They're 30 percent higher, on average, if you book less than a week before summer's last hoorah.

But how can two holiday weekends so close together have such different rules for snagging cheap fares?

Look at the calendar, said Expedia analyst Daniel Kissin. Fourth of July, although it's more of a popular driving holiday, still gets loads of people in the skies every year. Labor Day isn't as popular because it usually coincides with back to school.

Following the old fashioned rule of supply and demand, it makes sense to book early for the most popular travel holidays: Thanksgiving, Christmas, Memorial Day. At other times of the year, it's better to gamble and hold out for that cheaper fare closer to your travel date.

The rules of low fares are evolving quickly as airlines recover from the recession. Last year, procrastination was the name of the game. Because travel demand was sluggish, airlines discounted seats or launched fare sales close to flight time. But this year, travel demand is inching up and airlines have slimmed their fleets — the perfect equation for higher fares.

Certain destinations also have different rules. Procrastinators with island dreams, listen up: That flight to Hawaii will be cheaper the more you wait. The reason? Hawaii is a more expensive destination, so travelers tend to book earlier, Kissin said. If flights aren't full within a couple weeks of departure, discounts are bound to pop up.

The same could be said about flights to Europe, Asia or other overseas hot spots. A cheaper fare might be a few days away.

When you're ready to book that flight, don't forget to book the hotel, too. Expedia spokesman Adam Anderson said booking separately was one of the biggest money-losing mistakes people make. Reserving everything together online could save you hundreds of dollars, depending on the total price of your trip.