Here's my biggest Southwest tip. Building on what others have suggested, i.e. booking your tickets online for the double bonus, book double sets of round-trips. Let me explain. If you are flying from Kansas City to, say, Baltimore, book a round-trip from Kansas City to Nashville. Then book a round-trip from Nashville to Baltimore. Often the cost of doing this is $10-30 more than just booking the one round-trip from Kansas City to Baltimore. And with the double bonus, you'll get a free ticket for every two trips you make, i.e. if you do this twice -- Kansas City to Nashville to Baltimore to Nashville to Kansas City -- you'll get a free ticket. Not too bad.