Concentration, quick reactions, and confidence.
To play successfully up the middle, you have to want the ball to come to you, you have to know you can handle it - whether it's a high hopper, a slow roller, a deflection off the lip of the grass or a quick scooter through the dirt at your feet.

That confidence doesn't come from wishing, it comes from practice - whenever and wherever you can. And remember: concentration doesn't just mean tracking the baseball, it means all the thinking you do before the pitch... watch the catcher for signs, size up the baserunners, and check coverage responsibility with your middle infield teamate.