Andy Segal said:
This is great advice. One problem with this, I've found for me, is when I'm playing in a daylong or weekend long tournament. If I concentrate as Andy says, on the first few matches, then I'm sometimes too tired from that intense focus to concentrate the same on matches later in the day.
One way I've helped with that is to allow my concentration to rise and fall during the shot. If I put full concentration at the beginning of my shot and then let it fall somewhat on the last ingredient of the shot, I can "pace" myself better. This then "saves" me some energy, if you will, to use on those 1:00 am matches, without costing me this match.
Also, nutrition helps. Blood sugar levels have a profound effect on the brain's immediate workings and other nutrients help the brain in the long-term. Take this seriously, imho.
It is said there are 3 things that cause concentration troubles:
1.) MOTIVATION...If you don't kinow why your shooting this shot, then why concentrate on it? This harkens back to the thread on 'what makes a good player' that appeared last week I believe, where I talked about my definition of a good player is one who makes sure that this shot adds to his happiness. This integration makes me concentrate at will (or not, at will), because the "biggest picture" is the most important part of this teeny tiny little shot.
2.) INTERNAL DISTRACTIONS...This is what the so called "pre-shot routine" eliminates. As for Monk's book, it did nothing for me here, but maybe that's just me.
3.) EXTERNAL DISTRACTIONS...These are uncontrollable, but can still be handled with some success. I'd suggest Albert Ellis' book: The New Guide for Rational Living, copyright 1975, Melvin Powers, Wilshire Book Co, Hollywood, CA where he convinces the reader that outside forces happen, but YOUR reaction to these is totally up to you---Totally! Have you ever seen one guy get mad and lose concentration from a sharking, but another guy right there with 'em doesn't? The same outside force, but totally different reactions (and effects) from the two players. Each chose his reaction.
I forget where these three things came from ( a psychology book, maybe?), but understanding them sure helped me. I hope they help you, too.
Jeff Livingston
. Maybe that is perfect concentration, not deadstroke, but "just doing it". 
), Usually i (all in usually a split second) compute the shot it self, the angle, adjust that angle for speed, stroke, deflection and throw, all before i get down, and sometimes in mid-stride going around the table to the shot.