The closest I've ever come to catching a foul ball was in Seattle, at the Kingdome. I was sitting dead center behind home plate, about halfway up in the upper deck. The Mariners hitter had his timing right, but just got under it, sending the ball rocketing directly towards our section. A fan maybe four or five rows in front of me snagged the ball, but here I am, 15 years later, entirely convinced that had the ball glanced off of his hands, it would have ricocheted directly too me. You can't convince me otherwise, and that is the closest I've ever gotten to a ball.
This is a roundabout way of saying that will probably never in your life catch a foul ball, and you may not even get a chance at one. (Unless you're an asshole ballhawk like this guy.) The opportunities are few and far between, and if the moment comes, you had better be prepared to grasp it, or live out a life of regret.