The First Rule of Warfare is that the "First Rule of Warfare" is always the First Rule of Warfare.
You may have heard that the First Rule of Warfare is... [insert actual advice here]. ie.; don't attack a stronger enemy, there's no such thing as overkill, the weapon is always loaded, etc. They're all the First Rule of Warfare.
I suppose that depends on which book you're getting the rules from.
I always heard that it's "all warfare is based on deception".
The first rule of Tautology Club is the first rule of Tautology Club