1. High level of marksmanship ability via Skill and Equipment
2. High level of applied tactics and concepts via proper and complete force on force indoctrination and associated disciplines
3. Complete understanding and internalizing of real world ROE via memorization and daily exercise of the Flowchart of Justified Deadly Force
4. Gentleman Warrior self-image that sets the stage for the requisite mental attitude, and simplifies action.
Have those four...really have them, and any active shooter (crazy guy or jihadist) that targets anyplace you happen to be standing, is in far more danger from you, than you are from him.