Book in advance—or at least book at the best times. It's best if you can book your trip at least 45 days in advance, says CheapOair's Mark Drusch. If that's just not possible, "airlines do tend to launch major fare sales late at night," says Drusch. "Plus, leaving on a Saturday can be a cheaper option for travelers as opposed to Fridays and Sundays.
Something else to keep in mind—sales for flights are generally put up online on Tuesdays, and airlines try to match sale-for-sale, says Gillian Telling, mom and editor-in-chief of "Budget Travel." "Also, keep in mind that even though kids under 2 fly for free, in some countries they are still charged a tax. When we went to the Dominican Republic, we had no idea that we'd have to pay $150 at the airport for our son, but they wouldn't let us on the plane otherwise."