many 40k players assert that you cannot apply the principles of such military theorists as Sin tzu, or Von Clausewitz to the game. They cite the abstract nature of the game, or the age of the strategy compared to the setting's age and technology.
I say that this is bull. They are committing one of the greatest sins a military leader can commit: The sin of thinking within too limited a field of view. By looking at the theories in a very literal light, or by believing in the fallacy that technology can change the fundamental nature of warfare, they are allowing a useful tool to go unused.
As for the " abstraction," it is also fallacious, as all wargames, fantasy or historical, are based upon the military practice of using sand tables, along with symbolic tokens representing various units, with an expected table of organization and equipment. This practice is used to develop and teach solutions to various military problems, and to plan for warfare. Since the principles apply to the latter, with it's abstractions, they are just as applicable to the former.
Von Clausewitz's nine principles were: Mass, objective, offensive, economy of force, maneuver, unity of command, security, surprise, simplicity
Mass is as simple as having enough men at the point of contact with the enemy to overwhelm the enemy and cause teir destruction
Objective is to have a plan, and stick with it, avoiding becoming entangled in chasing opportunities that can distract and delay your forces.
Offensive is to always go on the attack.
Economy of force is to avoid committing more men than is necessary to do the job, or not using an artillery piece when a rifle will do the job equally well, but with a reduced cost in matériel.
maneuver is to place your men where they can do the most damage, or avoid damage until they can strike the enemy.
Unity of command is to ensure that all of the components of your force are working together to achieve a common goal.
Security, is both physical, such as not allowing the enemy to infiltrate your camp, but also more abstract, such as preventing the enemy from seeing your plans.
Suprise is the goal of misleading your opponent into making false assumptions regarding your forces or strategy.
Simplicity, the best plans are those that place as little as possible to luck or timing, and therefore are as simple as possible.
In outlining the nine principles of Von Clausewitz, I simplify, but the basic ideas are preserved. The way that this is applied on the table top is to not be literal in their application, but to use them as Von Clausewitz intended, as principles to guide your conduct. Instead of building "death star" units, that usually are either too powerful and therefore are overkill, or spamming foot troops, but without any supporting elements to ensure that those foot troops manage to get to battle, Take the middle ground, wit enough manpower to still overwhelm the enemy, but still avoiding overkill that consumes points, but does not necessarily cause a commensurate destruction of the enemy.
By taking a broader view of Military theory, I believe that they can not only be completely relevant, but can vastly improve your performance on the table top, regardless of ruleset.