Why does dell1972 reminds me of derek2010?

Anyway, to answer you since you asked, there really isn't. It depends on where you are, where you are going, when, etc. Usually general rule of thumb is buying early, scan/wait for low fares, ask a good travel agent to keep a good monitor for you. For example, you can ask a good travel agent to buy a ticket from point A to point B only if V fare comes up (assuming you want the miles) or as even wait for N fare!