1: Use a search engine
I always start my search by using a search engine. A search engine will give you the best variety of prices from different airlines. It’ll scour the internet in seconds, to give you the best possible prices out there. You can use filters if you have any specific airlines you want to travel with or filter by travel time. You will always get the cheapest possible journey up first, but the travel time might be 30 hours due to long transfer times. Filters will hide the flights that doesn’t meet your criteria.
I personally prefer either Momondo or Skyscanner. There are several search engines out there, use whatever search engine you prefer and save time while hunting down the cheapest airline tickets. Before booking through an online travel agency, I always make sure to check the prices of the airline’s website. I do this because I want to make sure I get the best price out there, but my main reason is this: Booking a flight directly from the airline will give you more leverage in case of changes, cancellations or delays. I always try to book directly, but if it’s far more expensive, I just book through an online travel agency.