Rule Number Four
Rule Number Four is to be sure of your target and what's behind it. In the case of a mall shooting, it's almost virtually certain that there's an innocent person behind the shooter. If he's standing in front of a wall, it's probably drywall with shoppers on the other side.
Where to run to: every store has at least one emergency exit in addition to the front door. Run in a store, head to the back. The fire exit may be alarmed, but that's OK. I'd feel a lot better running through the parking lot than being in the mall with a shooter.