If you want to become a comedian, the most important quality beyond sheer talent is perseverance. Many comics who appear to be overnight successes actually spent many years honing their stand up routines in any comedy club that would give them a stage. The best comedians are those who didn't give up even when they were booed by their early audiences.
Career comedians learn as much from their failures as they do from their successes. They learn how to make the crowd laugh and how to time a joke just right. Most of all, they find the material that works for them and put their own unique views, attitudes, and background into it. If you want to become a comedian crowds appreciate, learn how to give them a sense of who you are by making fun of yourself and your background a little.
Start getting up on stage at amateur open mic nights. Make note of your successes and learn from your failures. It's a good idea to keep a notebook to jot down ideas and just little things that come to you if you want to become a comedian. You never know when just a small idea will inspire a whole comedy stand up routine. How you look at the world differently than others can make your comedic material interesting, fresh, and funny.
Practice delivering your material in different ways — quick versus slow for example. Watch comedians you admire and learn from what they do. Don't copy their methods, though; you'll have to find your own style of communicating to the audience. If you don't feel relaxed in front of the audience, consider making jokes about how nervous you are. Use these jokes to segue into your other material.
While there isn't any formal education or training to become a comedian, there is a sort of apprenticeship among stand up comics. Well-established comics will often let newer, aspiring comedians open their shows. This was the case for comedian Jim Carrey, who, at the start of his career, opened for the much older more experienced stand up comic, Rodney Dangerfield.
If you want to become a comedian, you'll have to keep performing in order to get accepted for paid gigs by comedy club owners. Doing well at contests and amateur nights can be a good way to eventually get paying gigs, but you will have to keep trying in order to get booked into popular comedy clubs. If you keep doing the stand up comedy you love, even only on weekends to start, eventually you may get noticed by people who can accelerate your career.