Shop early as airlines tend to sell tickets at the lowest prices several months in advance. The longer you wait to purchase your ticket, the pricier it will be.
Be flexible with your travel dates. Your flight one day might be twice as expensive as it is if you leave on the same flight a day earlier or later.
Shop around. Compare prices and airlines. This is where travel search engines comes in handy. You provide your travel information: desired airports, dates and the number of tickets needed and they'll provide you with a list of all the flights between those two airports. Narrow down your choice by price.
Check with your airline directly. Sometimes finding a cheap flight on a travel site might seem like the cheapest flight, but booking the same flight directly through your airline may be less expensive.
Change airports. Many cities have several airports within a very short distance of the city, and changing your arrival airport will reduce the cost of your flight. For example, if you're flying into New York City you can try JFK, LaGuardia or Newark Liberty airport. All are about the same distance into Manhattan, but prices to each vary greatly.