Time is the most important factor here. The best way to guarantee low-cost flights is to book a few months in advance. Waiting for last-minute deals is riskier and might not be effective, as airlines can often save a few seats on the plane for people who are not flexible with their departure date. The cheapest airline tickets will always be found several weeks before the planned journey. It's best to book just when the new connection sellout begins. This is when the carriers fill up the plane so that they can introduce new customers to their brand, or gain loyalty of existing ones.