To help prevent or minimize incidents, there should be a federally-funded program for law-abiding citizens who wishes to obtain firearms, first aid, risk assessment, and situation training.
This will hopefully encourage personal carry of firearms and education to allow most citizens to be able to IMMEDIATELY and EFFECTIVELY assist in situations where deadly force may be necessary as well as first aid until official law enforcement and medical personnel arrive. Hopefully, this will minimize casualties in future incidents as well as promote the responsibility to look out for your fellow citizens in cases of dire need.
Training should practice immediate health care, safe and effective use of a firearm, how to react to given situations, and working with others to diffuse incidents quickly.