You need an acute understanding of the game, its rules, and how to execute offensive and defensive strategies. You must be able to teach the skills of the game to amazing athletes who might slip into bad habits. You must be fair, approachable, organized, and able to keep large groups of people happy when they are tired, stressed, and lonely.
No major league franchise will hire you without having confidence that you embody these characteristics. Your résumé must show a successful career as player and coach. Getting a shot at being a major league manager is less likely than playing for a major league team. Most players hang up the cleats after high school, and the rest trade in their baseballs for softballs after four years in college. The truth is that the elite players get drafted before their 19th birthday, don't go to college, and spend years in The Farm System…not like "moo," farms, it's just a euphemism for all the minor league teams affiliated with the major league team. Most franchises have at least six farm teams that they can pull from, so the odds are slim of making it to Wrigley, Fenway, or Yankee Stadium. What do lightening strikes, shark attacks, winning Powerball, and playing in the major leagues all have in common? Long shot.
Knowledge of the skills and some success as a player are still not enough. Teams hire proven winners and proven leaders. So win some Gold Gloves, MVPs, World Series, and batting titles. It might be good to be a team captain as well. Then you can start your coaching career.