"Your livelihood in sports is very short, in your 30s they're talking about retiring you, and then you've got a life after that," Johnson said. "So make the best out of it while you can."
He also warned the players to stay away from drugs and anything that could damage their health.
"We lose so many athletes today because they want to look good ... it's not about looking good, it's about playing good," Johnson said. "It doesn't necessarily [matter] the size you are to be good.
"I'm a little cat, 165 pounds. I hit the home run to win the world championship for the Dodgers in 1965 ... and then I went back and played in another series, and I got two more world championship rings. They didn't come out of a Cracker Jack box, guys. They came from hard work, and that's what you're going to have to do."
Johnson encouraged the players to take advantage of the opportunities in front of them, including having the chance to meet and play in front of MLB executives and scouts during the tournament.
"Let this [RBI World Series] be a stepping stone. You guys have got the most wonderful opportunity to make it," Johnson said.
Garcia and Rieker gave a demonstration of the strike zone and tips on working with umpires and respecting the game. They explained what it's like umpiring in the Major Leagues, and encouraged them to think about umpiring as a career in baseball as well.
"I hope that they realize that there's other avenues in baseball," Rieker said. "We hope that people that have good baseball skills and knowledge say, 'I still want to be a part of the game, I want to be an umpire.'... It's a really rewarding career, and we hope that we touched some future umpires here today."
MLB's Urban Youth Academy will host umpire camps in November for people interested in learning how to pursue umpiring as a career. Anyone 18 and older can participate.
"Just people that want to learn more about the game, experience is not necessary," Rieker said. "We're going to have people that have been umpiring for 25 years and we'll have people who have never called a pitch. We'll take them all -- we'll gear the training toward them.
"Basically we're going to have fun. We're going to teach people about umpiring and hopefully it will open some doorways for some people," he said.
The players had a chance to work on their baseball skills in several team and individual events at the Workout Day, including a 60-yard dash, a catcher's accuracy throw, an outfield relay throw and an around-the-horn relay.
Tyler Griffith, 14, from the St. Petersburg Juniors RBI team, said he had fun at the Workout Day events. This is his first RBI World Series.
"I think [the Workout Day] was good," Griffith said. "It was fun, competing against other teams and showing them what we've got. I liked how they showed us the umpiring and how they train -- how they judge [strikes]."
He said he enjoyed hearing about Johnson's career in the Major Leagues and how he got there.
"I thought it was cool ... [Johnson] telling us how you've got to work hard and just keep going, and how he was in the Minor Leagues for a little bit and then he just kept working hard," Griffith said.
Avis Smith, 18, from the Philadelphia Seniors RBI team said he thought his team did well in the events and he liked hearing from the speakers.
"They were very informative, especially the umpires, elaborating on the strike zone," Smith said. "I thought it was pretty cool [to see Johnson], it's good to see legends."
He said this is also his first RBI World Series and he is enjoying the experience.
"It's really nice, you get to do a lot of stuff, and play some good competitive baseball," Smith said.