The very first tip is to be flexible with your travel date and time. The day plays a major role if you get an expensive or cheap airline ticket, for all airlines. Once you have decided the destination, check for flights online or any flight booking portal and check when you can get the cheapest airfare for your destinations. Then plan a trip according to that date & time, and book as early as possible, because early birds get to enjoy unmatchable low airfares.
You must think “maybe if I wait just a little longer, prices will drop,”, but that is not how the airline market works. You can get cheap airfares for all airlines if you book flights early.
Also, if you want to travel at the time of a festival or vacation time then you may not be able to book cheap flight tickets, because everyone will be flying at that time, thus the demand and flight fare would be high.
For example: August is a month of festivals, so traveling in Europe at that time would be super expensive. But if you want to visit Paris, the best time would be the fall/spring season as you get cheaper airfare options.
So, fly off-season and book flights as early as possible to enjoy cheap flights without any compromise on comfort.