Most countries in the world boast an airline that is a national carrier that plies international routes, and not just between its cities and other countries, but between cities outside its borders. This can be described as a major airline.
The first step to picking which carrier you are going to book a ticket on, is deciding where you are traveling, be it for business or for a vacation. You then do some research on the internet or by consulting travel agents to know which major airlines travel from where you are to your desired destination. You can then research or find out about each carrier from their websites or from the many consumer review websites that are available.
Upon deciding on the airline that you are going to fly, you will then need to define a budget. Are there any flights available on the day that you want to fly, that are within your budget? If not, what the closest days available or the next best options are in regards to flight.
You also want to consider where you will have your lay over when in transit. Do you need to get any transit visas? Some major airlines will organize these for you if you request it. You can even pick an airline with an overnight layover in a city you have never been to. They often provide hotels for the travelers to spend the night in. you can take in the sights and sounds of this new city during your layover.
Pick only the major airlines that are reliable, and if you are a frequent traveler, you can even pick one with a reward system. And you can redeem your points in hotels, grocery stores or even when picking a new destination to fly to.