Where can I find cheap air tickets?

I usually book tickets in advance, it saves a lot of money, also I know that cheap air tickets can be found at the last minute, for example here www.iflyfirstclass.com/page/last-minute-deals . You can also check the prices for air tickets in different airports. I know that many airlines reduce the prices for flights, if they are in the middle of the week or unpopular time. You can search for useful tips in travel blog, there is a lot of lifehackes on travel.