There’s so many way to book flights online, that it can all be overwhelming when and where the best sites are to buy flights from are. From my experiences traveling, I actually only use 1 app called Hopper (both on Android and iOS).
Hopper is an app that tells you when the best time to buy flights are. The way it works is very simple: you first select your destination, then select the travel dates you want to travel on. Hopper then uses an algorithm to actually predict what the lowest flight costs would be based off of historical data. It will then either tell you to wait or book now. If it says wait, you can add the flight to your watch list. Hopper will notify you on your phone of any price changes and will tell you when to book your flight to get the best deal, which sites like Kayak and Expedia can’t offer.
Here’s the way I actually use it. I pick a destination I want to go to at around a certain time of the year. Then I add multiple possible travel dates to my watch list. If you do this, you increase your chances of Hopper finding a better deal for you. For example, I booked a flight to Japan this past winter and I set multiple travel dates: 12/26-1/4, 12/27-1/5, 12/26-1/6. By doing this, Hopper notified me that the 12/27-1/5 dates were priced cheaper than the others. I was able to book my flight for these dates for about $100 cheaper than if I would have booked the other dates.
One other trick is that I don’t actually book flights off Hopper. I go to the actual airlines websites and put in the exact dates I have in Hopper to see if I’m getting the best price. Sometimes the airlines will have an even better price than Hopper (maybe like $20 off). I think this is just because Hopper hikes the price a little bit just so they make a profit.