Major airlines all offer frequent flyer programs which award miles or points for air travel. Are you an ideal candidate for these programs? If you fly often, these miles can accumulate and offer perks such as upgraded seating or free travel. However, if you only travel occasionally or don't have particular loyalty to one airline, you may not receive many benefits or even lose your miles after a year of inactivity.
Every major city is a hub for a particular airline (American Airlines in Miami; Delta in Atlanta; United in Chicago; Southwest in Dallas). If you live near a hub and are loyal to that carrier, you can quickly accumulate airline miles. Of note, if you fly any airlines within the Star Alliance, only sign up for one frequent flyer card within the alliance: United, Lufthansa, Air Canada, Thai Airways, ANA, and others (note that United has more tiers to offer the best perks to road warriors). Another large alliance for international travelers is Oneworld, with carriers such as British Airways, Iberia, Japan Airlines, Quantis, and others. Again, only hold one card for use with all Oneworld carriers to maximize your mileage balance.
Airline credit cards can offer 'free' miles, which can be exchanged for free flights or upgrades. However, these free miles and the miles you earn while using the card typically do not boost your status within the frequent flyer programs (i.e., the more you fly, the higher your status and better perks you will see, such as shorter checking lines, priority boarding, or even lounge access). Also, most of these cards include high annual fees. Also, some hotel programs also allow you to build airline miles, such as the Hilton Honors program.
The airline industry is in the process of evaluating reward programs in an attempt to offer more perks to gain new customers in lieu of the traditional system of rewarding loyalty. Always read the fine print and stay tuned or subscribe to learn about any major changes to frequent flyer programs as they happen.