In my studies of military strategy, the most important idea I have learned is known as the "indirect method." This method basically describes that a direct attack against an enemy is never beneficial, even if your army outnumbers theirs. A direct attack means that you are attacking the enemy where they expect you. They have prepared for this exact route of attack and how to best defend it. The indirect method describes that you should always look to throw the enemy off guard. This is usually done with the positioning of your army. If you can get behind the enemy, or break the middle of an army, then you have thrown off the enemy, they are unprepared for what they are presented with, giving you the physical and psychological advantage.
Beyond positioning, the other ways to gain an advantage over your enemy are by having an innovational weapon or method, being aware of the movements of your enemy, and by reacting BEFORE your enemy acts.
Looking at some of the great leaders in miltary history can show us how they have become successful.
Napoleon is a good one to look at. Napoleon did a number of great things to become the powerful dictator and great military leader he is known for. Particularly, for the focus of this blog, he used the indirect strategy to always keep the enemy off-balance. For instance, Napoleon would attack an enemy's flank, forcing his enemy to focus some troops on this new threat. After the opposing army separated their troops, he would send a hard attack to the middle of the army, breaking it in half, giving Napoleon a physical and psychological advantage and forcing the enemy to surrender or flee.
We shall go into some other great military leaders on some later blog posts and how each was successful with their strategy.
The indirect method (as well as the great military leaders) is described in great detail by B.H. Liddell Hart in the book "Strategy". It is a great resource in learning more about this mindset and how it has been used by the great military leaders throughout history.