First, "buy your flights at 12:01 Wednesday morning in the time zone where the airline is based," says Peter Greenberg, a travel expert for AARP.
"How it works: You benefit from travelers who booked their airfare between Friday and Monday, when most airline fare wars are announced, but didn't pay within the required 24 hours. On Tuesday at midnight, those unbought discount fares come flooding back into the airlines' computers, so that's when you pounce."
Also, fly on off-peak days and times. Go on Tuesday, Wednesday or Thursday and at midday, rather than the beginning or end of the workday. Not only can you save money but you might actually have a little more room.
Consider alternate airports to the major hubs. For example, the main airport for Washington, D.C., is Ronald Reagan Washington National, but Washington Dulles International and Baltimore-Washington International are both within 45 minutes of the city and might offer better fares or scheduling.
If you're willing to use a cab or a city's public transportation, you can save dramatically on rental cars by booking through locations beyond the airport. Airports charge additional taxes and concession fees to cover shuttles and other costs — these do not apply at standalone locations.