Tuesdays and Wednesdays are usually the cheapest days to travel. This means a one day, six day or eight day trip, which isn't always possible. But even if you can only travel one leg of your trip on the cheaper day, you can still save a bundle. Just make sure that hotel and food costs do not exceed the savings if you wind up having to spend an extra night at your destination.
When you are searching for airplane tickets, broaden your search by looking at alternate airports. For example, if you are flying into Cincinnati, Ohio, Delta's Cincinnati hub means that it dominates the airport (which is actually in Covington, Kentucky) and inexpensive tickets are hard to come by. But the Dayton, Ohio airport, just 60 miles away, offers low cost flights on a number of airlines, and easy access to Cincinnati's northern suburbs. Car rentals are also less expensive here.
If you want to go to Aspen in winter, London during the Olympics or Washington, DC during cherry blossom season, your options for cheap flights are limited. But if you are going to Florida or the Caribbean in summer, Los Angeles during "June gloom" or Niagara Falls in January, you can find cheaper airplane tickets. The shoulder season, just before high season, often has the same weather, but is much cheaper.
You can check airline websites for flight sales, and comparison shopping sites like Fly.com and Kayak.com. On Fly.com, you can actually book your flights; Kayak.com just lets you search for flights, but is not a booking agent. Each comparison site is limited to the airlines that let it list its flights. Jet Blue does not allow its flights to appear on Kayak, so you will have to check that site out separately.
