Check out kayak.com. Check the airline's site for the fare you like there. Check Southwest's site to see if they fly where you want to go (remember they don't have extra fees). If you have more than about 3 few months before your travel, wait for a month or so and see if you can pick up a sale price. Be sure to check a few days around your planned dates to see if there are better fares on a different date. Fares can vary daily. That's my usual routine. You might have other low-fare airlines you should check directly. Not all of them are on the general travel sites.