Sacrifice Your Time
Becoming a professional baseball player requires thousands of repetitions, known in the game as "reps". Sports science lets us know that a batter can't even see the last half of a pitch's trajectory to the plate; that hitting a professional fastball amounts to good guesswork, and that's where the reps come in. You need to know how to track each pitch so you can swing at where you know the ball is going to be. And you only develop that kind of foresight with thousands, perhaps millions, of reps. Start young, play and practice as much as you can, stay committed and be willing to sacrifice social-network-worthy experiences with your friends.
Sharpen the Specific Tools You Possess
Baseball measures position players using the five-tool system -- hit for power, hit for average, foot speed, throw-arm strength, and the ability to track and catch the ball. Superstars possess all five tools, but you can go pro focusing on just a few. Or you can scrap playing a position altogether and focus on pitching if you have great arm strength. After a couple of thousand reps, you should have a good idea of what you excel at. Devote a majority of your practice time focusing on those skills. Seek out a professional coach that specializes in the tools you are trying to sharpen, because nothing accelerates development like gleaning wisdom from someone who has done it before.
Become a Professional Grade Athlete
Baseball is a series of explosive movements built on top of each other, and each explosive movement is followed by a period of rest and almost total recovery. You don't often see a batter get winded from swinging too much. So ditch the aerobic workouts, such as jogging and swimming, and replace them with explosive anaerobic workouts to build baseball-specific stamina. Get into the weight room to build total body strength, doing two upper back lifts for every chest exercise performed. Throw medicine balls explosively to develop rotational strength, invest in a good plyometric routine, run tons of short sprints, do lightweight rotator cuff exercises and get on a regimented throwing program to build arm strength.
Get Seen by Decision Makers
The most common way into the pro game is to get on travel, school and scout teams in high school and college, be seen by Major League scouts and get drafted by an MLB organization. But that's not the only way in. Plenty of players sign as non-drafted free agents out of open tryouts and through recommendations from former pros. Plus, there are dozens of professional independent league teams across the country; teams that pay and play like the minor leagues but are not affiliated with an MLB organization. And even more players are "picked up" by MLB organizations out of independent leagues throughout the year. Dig deep, find decision makers and get seen by them, whether at an open tryout or by just showing up and demanding to be seen. Professional baseball is designed to make the cream rise to the top. Simply put -- if you are good enough, you'll get signed.