Make Yourself Useful
It makes sense to be an expert on your position in baseball; every position, after all, has a specific purpose and a way it's most effectively played. But what's even more useful than being the master of your baseball domain? Being a master of many domains in baseball.
A person who can play several positions -- called a utility player -- can be a great strategy to ratchet up your game. Not only is learning the nuance of each position useful in offense, it's also a way to understand the weakness of each position when you're hitting.
Even major leaguers will often try to extend a career by switching positions or acting as a kind of "fill-in" utility player when the lineup demands it. A once-sharp (or perhaps simply acceptable) first baseman who isn't so fast on his feet but can still hit the ball over the fence might just be a great designated hitter in his golden years. Managers love having a player that they can sub into almost any role. If you've got someone who can fill third, right field and first on any given day, it's like adding three players to the roster.
So while you should never slack off on practicing the position you love or that comes naturally to you, allow yourself to rotate. You might improve your game.