What do you do to become a professional video gamer
First, choose a game you particularly like and/or are very skilled at. Make sure you are good enough at the beginning to at least keep up with some skilled gamers.
Next, practice, practice, practice! Learn new techniques, skills, moves, etc. to make yourself a better player. It is always better to improve your playing instead of just jumping in competitively.
Once you think you are good enough to play the best, try to start playing competitive. Gamebattles.com allows you to play teams online for dozens and dozens of games. Play gamers that go to the website. Try to team with people and get better.
Usually it takes a lot of time to really get good. Once you think you are truly good enough, get on a good team (unless the game of your choice is individually played) and try to go to events hosted by Major League Gaming or World Cyber Games.
If you are truly good enough, you'll rise in competitive play and hopefully, one day, become a pro!