"Even a hawk - can be an eagle amongst sparrows."
Practice. Not shots. But that part of your brain that says, "I only need to sink THIS shot." Fawgettabowt what happened BEFORE this shot.
Fawgettabowt what might follow.
Think only about the shot before you - and turn off all the chatter, noise, silence, distractions around the shot that's before you.
THAT, takes practice!
I find playing loud music that I hate (like head-banger tunes) force me to separate my head from self-induced tension, like the annoying music, that results in an inner calmness and my emotions wane dramatically - as I get into the "zone."
The "zone" - what a great place to be in! And practice, can develop THAT phenomenon. Some would call it concentration. It's really not concentration of the task at hand but rather, turning OFF the extemporaneous distractions that surround us.
Trying to concentrate is like herding cats. But by eliminating attention-competing "noise" - concentration comes naturally. I find telling myself EVERY practice shot I make, is extremely significant - I can get into the zone.
When league play comes, I turn everything off but the shot now before me. Sort of like Tiger Woods dropping a 25' putt. He's not thinking about anything but the ball, the line and the cup. At the moment of contact, he doesn't know who's winning or who's watching. It's the same every time. The ball, the line, the cup...