1. Be flexible.
Opt for mid-week, mid-day flights when possible; skip large hubs in favor of smaller, alternate airports that charge less in taxes and attract low-cost carriers; and search up to three days before and after your ideal departure and return dates.
2. Always peek at roundtrip airfares.
Even if you're booking a one-way ticket, the roundtrip may cost less. (Just make sure you're flying on the outbound portion of the ticket. If you don't show up for that, the return will automatically be cancelled.)
3. Set up automatic fare alerts.
Airfares change periodically during the day. You don't have to keep checking back-let the search-engines do the tracking work for you and arrange to have e-mails sent to you when fares fall into your desired range. Start with Airfare Watchdog. (http://www.airfarewatchdog.com/) It spots bargains from Southwest Airlines––not all aggregator sites do.