The first most important thing you need to know, is that you won’t find 20$ tickets in July August, especially if you decided to buy them in May-June, so the first point is to start planning NOW your summer adventure if you want it to be accessible.
There are three main seasons in the tourism industry: high season (mid June- late August, Christmas time), mid season (easter and March- May) and the most important one low season (September-November, January- February).
The following rules are pretty universal for all the airlines in the world:
HIGH SEASON: pretty obvious, but high season is the most active one, is this time of the year when everyone can and want to travel. It’s always summertime and Christmastime, as those are the times when everyone wants to relax on the beach and/or stay with the family. As more particular, high season can be considered some very popular events in a certain country i.e. the Brazilian carnival, st. Patrick’s Day in Ireland or Oktoberfest in Germany. That’s the time when the companies can manipulate with the tickets the way they want, as everyone will anyway buy the tickets.
MID SEASON: that’s usually before or right after the high season, or some smaller holidays, which some time coincide with the small school vacations, or some national days off i.e in Ireland it’s bank holidays. A type of mid season would be 1st of may in Germany, or 8 march in Russia, especially when they are end or beginning of the week. In the mid season ticket prices are pretty reasonable, but still more expensive than in the low season.
LOW SEASON: or simply- my favourite one. It occurs in the time when nobody is taking vacations because either there are no holidays, either bad climate conditions, either people simply don’t have money. Some dates? It’s October-November and January-March, last year there was the record price that I saw, ryanair was giving a 1£ ticket from Bucharest to Rome on 11 January, and 1£ from Rome to Bucharest on 21 January, so you could spend as much as 2£ for a 2 hours flight to Rome and Back. The problem of this season is to find your days off, and to not let yourself tempted by the typical seasonal holidays. It is true that you can find 10$ tickets all across Europe, and less than a 100$ all across US in this time.
Let me know what else are you curious about.