Search multiple sources, check fares frequently, use frequent flier miles, and consider flexible flying options to find the best fares. Airline fares change often, so finding the lowest rate often takes patience.
Checking the airline itself and other sources such as Expedia or KAYAK gives you a general idea of the options available. Many discount airlines such as Allegiant provide additional resources for finding cheap fares. Check both round-trip and one-way flights to compare costs. In some cases, you can get two one-way tickets cheaper than a round-trip fare. If you have flexibility in your travel dates or times, you may find a lower rate by going a day early or waiting a day later than planned. Flying from a different airport within driving distance is another way to save money.