✓Almost every "secret" to a cheaper fare is folklore. The only timing that matters is how far ahead you book.
Fares move on real supply and demand, not on your browser history. A VPN, incognito mode, clearing cookies, booking on a Tuesday or at midnight, hitting search one too many times: none of it changes the price. We've tested it, and so has everyone else. The cards below are the "hacks" that get shared the most and hold up the least.
The timing that does matter is how far ahead you book. The day of the week and the hour don't come into it. Roughly one to three months out for short-haul, two to six for long-haul. Don't leave it to the last minute, and don't book a year ahead either. Set a price alert and buy when it dips into a range you're happy with.
A couple of safety nets take the pressure off getting that timing perfect. On any flight touching the US, a Department of Transportation rule gives you a free 24-hour window to cancel most tickets booked at least seven days ahead, so you can grab a good price and sleep on it. And most US airlines have dropped change fees on everything above Basic Economy, so if the fare falls after you book you can often cancel and rebook at the lower price and take the difference as credit. Keep the alert running even after you've paid.
Two advanced tricks do sometimes work, with a catch. Hidden-city ticketing (booking A→C via B and getting off at B because it's cheaper) can work, but you can't check a bag, it only works one-way, and airlines can penalize your frequent-flyer account or cancel your return if you no-show a leg. Error fares (a genuinely mispriced ticket) are real and occasionally spectacular, but the airline can cancel them, so don't book non-refundable hotels around one until the ticket is actually issued: booked, paid, and confirmed by the airline, not just a booking-confirmation screen. Fly once a year? Skip both and stick to the tips above.