The art of war

is an excellent book by Sun Tzu (isbn 0-87773-537-9). As usual I'm going to quote from a few pages:
Victory in war is not repetitious, but adapts its form endlessly.
Foreknowledge cannot be gotten from ghosts and spirits, cannot be had by analogy, cannot be found by calculation. it must be obtained from people, people who know the conditions of the enemy.
The condition of a military force is that its essential factor is speed.
When they give out numerous rewards, it means they are at an impasse; when they give out numerous punishments, it means they are worn out.
Let diplomatic relations be established at borders.
Preparedness everywhere means lack everywhere.
Good warriors seek effectiveness in battle from the force of momentum, not from the individual.
Great wisdom is not obvious, great merit is not advertised. When trouble is solved before it forms, who calls that clever? When there is victory without battle, who talks of bravery?
Making yourself invincible means knowing yourself. like going to announce to your superiors that you want to put out a fire - by the time you get back with an order, there is nothing left but ashes.
It takes twenty pounds of provisions to deliver one pound of provisions to a distant army.