Once I have my dates picked out and hotel booked, usually 6 to 9 months in advance. With a price range in mind I start searching for airfare. I use Kayak, Vayama, and ITA Matrix. I also set up price alerts and fly mid week. I search at odd times and different days. The best fare I ever found was with a random search on a Saturday night. I caught a one day sale for half what they were the day before and after. When I find a price in or near my target I buy and don't look back. When possible I purchase through Orbitz because of their rebate policy.