Each airline offers many rewards for choosing them. Instead of using different airlines whenever going city to city, it is important that you use one airline, increasing your reputation with them and also building up a sort of credit system that they might have. Having a frequent flyer status associated with your name will automatically make you eligible to upgrade your airline ticket whenever possible and sometimes, even for free.
Talk to Ticket Agent
The ticketing agent is your gateway to getting the seat of your choice, which is why being patient and assisting through anything they may need is of the necessity in this case. If you treat your ticketing agent in a bad way and are known to be flaky in terms of making reservations, the ticket agent will also not want to assist you as much as they possibly can and will work towards satisfying someone who is consistent.
Frequent Flyer Miles
If you have travelled a lot recently, you can check with the respective airline on how many frequent flyer miles you have accumulated and what you are eligible for with that amount. Most people, who are constant travellers, do not take this benefit into consideration and end up losing out due to sheer ignorance. Such benefits are in place for loyal customers, which is why taking benefits from them is your right.
If you are able to find out that the flight you are about to board has empty spaces, asking to be upgraded on the spot is also an option. Some agents insert that option, which is dependent on availability of open seats so that the ticket handler can do the necessary.