How do mass attackers get so many kills? At every school I've been to I've always had a strategy. In a class room I always now where the nearest doors are, where the best conceal is, and where the closet objects for self defense are. Every possible exit to the campus is known. If I'm outside and I hear gunshots, I'll know where I'm going. Contingencies are also planned for multiple shooters.
It's also a good idea to know which direction the nearest police station is.