Airline fares will keep rising the closer you get to departure, but there is a sweet spot when the airlines begin to either lower or increase fares based on demand. Don’t wait until the last second but don’t book far, far in advance either. The best time to book your flight is around 6–8 weeks before your departure, or around three months before if you are going to your destination during their peak season.
Search flights from nearby airports. This is a very simple and effective trick to find cheap flights. Sometimes flights from local airport to your destination can be quite expensive while, on the contrary, flights from nearby airports can be really cheap. For example, international flights from Seattle are quite cheap when compared to international flights from Vancouver and the distance between the two cities is only 234 km (about a two and half hour drive). So driving or taking a bus to the nearby airport is sometimes a good way to get to your destination cheaply.
If your country’s currency is currently strong compared to others around the world, search airfare in a country where the currency is weaker. For example, the US dollar is strong and the New Zealand currency is weak. I found a one-way flight from Australia to NYC for $1,000 USD but when I searched on the NZ version of the airline, I found the same ticket for $600 USD. It’s the same airline, same flight, and same booking class. It was just booked in a different currency. This tip does not always work, but it works often enough that it’s something worth trying if your currency is currently doing well.
You're not crazy for thinking that a flight price has changed after searching it a few times in your web browser. Based on the cookies in your browser, flight prices do increase when a particular route is repeatedly searched, as the site wants to scare you into booking the flight quickly before prices get even higher. Always search for flights in incognito or private browsing mode to see the lowest prices.