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Pick the tallest guy out of the bunch. Works for the NBA, at least.

Interesting post. I've read Don Greene's methods as well...this question reminds me of a zen parable of some kind.
disciple: "Master, how do I know when I've attained enlightenment?"
master: "What is the sound of one hand clapping?"

I made that up but it's basically the same sort of thing you encounter. You are asking a question that has no answer because your mind is not in the right place to understand it. The 'trick' to finding your center is to SLOW DOWN and RELAX your mind. The moment you start thinking, "it's not working, why isn't it working", you're lost. Then you come on the internet looking for the "quick fix".

Don Greene's ideas are sound - they work. But like anything they require patience and practice. I recommend reading the book again, and try other books such as "zen guitar" and "the inner game of tennis" as well - they are all in the same ballpark. In general the key to finding your "center" is allowing the random thoughts in your mind to exist without disturbing your focus. So when you hear your mind say "this isn't working, this is stupid" or whatever, just let those thoughts float around but don't pay any attention to them - focus on taking a deep breath and relaxing. That might be a good place to start.
Good luck!

Read "Zen and the Art of Motorcycle Maintainence" by Robt. Persig (sp.?) It's a great intro to ZEN; and after reading it, you'll probably KNOW where your "center" is "at". "Zen and the Art of Archery" is also good entry-level Zen. That "one hand clapping" thing was good, No?