You may lower the price of a round trip air fare by as much as two-thirds by making certain your trip includes a Saturday evening stay over, and by purchasing the ticket in advance.
To make certain you have a cheap fare, even if you use a travel agent, contact all the airlines that fly where you want to go and ask what the lowest fare to your destination is.
Be flexible, if possible. Consider using lowfare carriers or alternative airports and keep an eye out for fare wars.
If you are a student or teacher, check out
http://www.studentuniverse.com* for specially negotiated deals.
*To be eligible to purchase from StudentUniverse, you must be either a student or teaching faculty member who is currently registered in an (government) accredited college, community college, or university of 2-4 years.