Also, look on flying on unstandardized days.
Monday morning, Thursday evening and Friday morning are business travelers, and fares are higher. Friday evening, and Saturday morning are causal flyers and are more expensive.
Tues, Wed and sometimes Thursday morning, along with some Sundays are generally cheaper, as there is less demand for flights.
Also, flights are generally cheaper in the 6 days before the 2 week window, when the remaining "unrestricted" restricted fares are released. these are the ones that say book more than 14 days, with no limit to the days. these are generally considered the deep discount fares. they are released and bought up quickly at the maximum days out, and when the airline cant sell the higher fares 3 weeks out, they deep discount them for 5-7 days, then inside the 2 weeks they will be back to being expensive.
there is a science to buying airfare, and the formula isn't consistent, because in a scenario where the flight is on a Monday morning, and its sold out to business fliers, that 2 1/2 week rule wouldn't come into play. This also depends on flight load.
So here is my advice for "best bet"
1) fly on a tues or wed
2) check fares when released and see if its a fare you are ok with
3) wait until half of the mark of maximum (if the airline only sells flights out 6 months, look at the 3 month date) and check the fares and open seats. If the plane is more than 3/4 sold 3 months out, you likely are not getting cheaper fares
4) wait until 3 weeks out and check fares and open seats
5) never buy inside the 2 week window
6) buy at times popular fliers wont fly. 5:30 AM flights, 10:30AM-2:30 PM flights
7) check alternate airports in the area, but adjust costs for the distance on other things you may have to purchase (rental car, hotel, cab, etc)
8) never pick the last flight of the day, or the only flight to that airport. this leads to you having to have no issues with not only your flight, but the flight that puts the plane at your airport.
From someone who flies 120 flights a year, I don't care about paying the extra for business flights, but this is the strategy I use to get upgrades, which is similar to watching price markers.