To buy a cheap ticket there is no universal advice on how to do this. Favorable prices for flights can be found both at the airline and at the agency; meta-search engines or even tour operators often have good discounts.
Therefore, it is best to know the algorithm by which it is best to look for cheap flights!
Check the cost on the websites of airlines that fly in the direction you need. It happens that they hold promotions and make discounts that are not available from their partners.
Check the cost through several different meta-search engines – Travelscompare, Momondo, Skyscanner. The price for the same destination with the same date may be different, as they have different conditions for working with airlines and agencies.
Use the calendar of low prices, it will help you find the days with the lowest prices in a given direction.
Use low-cost airlines in Asia and Europe, they can find a price from $10 per flight.
Change the point of departure and arrival, there are cities (those in which the airlines are based) from which departure is much cheaper, and getting to them by car or bus is not so difficult.
Sometimes the cost of a flight can be cheaper than flights with a connection. Try playing around with the search and have a little adventure in the new city. Very often, even at the lowest fare, a stopover of up to 3 days does not affect the cost of the ticket.
Charters often fly to tourist cities, and in order not to fly one way empty, they sell tickets for pennies for such flights, for example, where the regular cost is $100, you can buy a ticket for a charter for $30. Charters are also tracked in metasearch engines.