The best prescriptive book that I have found has been: http://www.amazon.com/Zen-Training-Philosophy-Shambhala-Clas...

Additionally I find that reading a good translation of the Tao helps, my personal favorite so far is: http://www.amazon.com/Tao-Te-Ching-Perennial-Classics/dp/006...

Did you ever tried meditation (I recommend zen style sitting, aka zazen)?

There is some nice, simple and to the point books about it, and for me it is something that really helps with concentration, sadness and focus.

list of good books

http://www.amazon.com/Zen-Training-Philosophy-Shambhala-Clas...

http://www.amazon.com/Zen-Brain-Understanding-Meditation-Con...

http://www.amazon.com/Mindfulness-Plain-English-Updated-Expa...