The nine principles of war are taken from Sun Tzu's The Art of War. The American military translates his Chinese into the following nine words:
You don't need to be in the military to apply these: anyone who plays real-time strategy computer games can also put them to good use. There are some who claim that these are also useful in the cutthroat world of business. None is more important than any other, however, common sense dictates that sometimes one may be the most relevant. If you have equal numbers to the enemy force, know their position, speed, and direction, and attack at a time, place, and from a direction of your choosing with everything you've got, then you have used offensive, surprise, simplicity, security, maneuver, and mass. However, if your goal was to capture their General, and he escapes in the ensuing carnage, then you have not used the principles of objective or economy of force to your advantage, and may have failed the simplicity test. Each of the principles is relatively simple to understand; however, if you want more information on them, I have noded the majority.
Those trying to memorize this list would be wise to use the mnemonics MOOSE MUSS or MOSS MOUSE.