I get a lot of questions about where I typically find affordable airfare. I am by no means an expert points/miles compiler, but I have a few go to sites that consistently help me find great flight deals.
First, be flexible. Many times when I'm looking for my next trip, I start my search where the airfare is already low. If I notice a dip in flights to Europe, I start checking my bucket list, and see what lines up. I often let the low price periods determine when I travel. If Asia is cheaper in January, I don't try to force it to work in the summer. This isn't always an option (if you need to book travel for a wedding, you obviously can't choose the dates based on your fare dips), BUT I would use it when you can.
Second, put out year round trackers. If you have a few trips coming up, or know you need to be home for Christmas or your grandma's birthday, start tracking them early. I always use Hopper. Is it perfect? No, but I almost always find it to be pretty spot on with flight price fluctuation. It lets you know if your flight price is expected to drop, rise, and when to go ahead and book. I normally have several of these set with push notifications. It helps to not let bookings get away from you, so you don't find yourself a week out with $$$$ blocking your way.
Third, use fare comparison websites. I find that Skyscanner is always the best bet. There are several companies that provide these services, but Skyscanner is the most stream-lined and user-friendly in my experience. You can search your dates and destinations once, and see hundreds of options on different airlines. It sometimes helps to check 'whole month', and see how much difference a few days can make. It is always exciting to see the prices drop as they scan!
Always search incognito. I cannot begin to understand why this helps, but I have seen it, and know it makes a difference. If your searches are anonymous, you often find better deals that hadn't revealed themselves in regular searches. This is especially relevant if you have repeatedly searched for the same flight a few times. Seems odd, but take it into consideration if you are not seeing changes in price!
Try to fly budget airlines. I have a love/hate relationship with budget air, but sometimes the deals are too good to pass up. Airlines like Spirit, Frontier, EasyJet, and others typically have great deals. You have to then take into consideration their exorbitant baggage fees, and other charged extras, and see if it makes the most sense for you. If you're traveling with multiple suitcases and baggage, sometimes it makes more sense to pay for a flight that allows luggage. Spirit even charges for water and carry ons, so utilize, but beware. Always read the fine print!
If your plans allow, volunteer to surrender your seat. I frequently fly between NYC and Atlanta, and will sometimes book flights I know will be crowded. These are most often early or late flights filled with business people trying to make it back for Monday morning. They often have overbooked the flight, and ask for volunteers to give up their seats for flight credits or cash which can be used towards future flights. I like to be one step ahead, and go ahead an let the gate attendant know I am willing to volunteer my seat, should the occasion arise. Then you are on their mind, and you have a better shot of being in the know before the announcement.