(I did do a search for previous threads about this topic... there were so many hits ((2500+)) that finding the old threads seemed steep time-wise)
People occasionally ask questions along the lines of "I can't seem to concentrate... what can I do...?"
Came across an old classic recently, Ernest Wood's Concentration.
Here is the Amazon on it http://www.amazon.com/Concentration-Pra ... B003DRNJC8
But, happily, here is the book: http://hpb.narod.ru/ConcentrationEW.htm
The first chapter is not so content-dense as the others, but starting with the second, there is some good practical advice and how-to-do-its. Then, just like physical exercise, the path is clear, it remains only to do it.