People say "Firearms safety" and training. Aside from SECURING YOUR FIREARMS that is not the issue. Safety training prevents accidents, not murder. Accidents are at a very low level. Training to know how to use a gun would logically increase the amount of death, as more shootings would be competent shootings, resulting in less wounds and more fatalities. The problems are crime (robbery assault et al), murder and suicide. In reverse order:
Suicide, non-forceful solutions;
1. Reduce "Shit Life Syndrome" by increasing social supports for families and individuals. That mean s food security, housing security, availability of healthcare, dental et al that can be accessed without a burden to the person. I think that UBI and government programs can do this faster in our existing framework then community based solutions but that's method, not solution.
2. Beyond securing the base of Mazlow's Pyramid, rebuilding community is key. That means creating a culture of inclusiveness, and non-hierarchal mentors and other supportive people. It means mental health services to increase coping skills and emotional healthcare. While these people are not mentally ill in a DSM-V way, the tools to help people before they choose to kill themselves by killing others are in the realm of mental health.
Murder, non-forceful solutions;
3. While the above will reduce both individual suicide and mass murder as suicide, there is an additional factor, Revenge. American society is built on the concept of retribution. Our system is built of using naked force to exact vengeance for wrongs. While the catharsis of seeing Rambo or The Punisher or even the courts harm people who've wronged them is great, it's creates a culture of violence as the solution. Combine that with individualist philosophy and a feeling of being ignored or unheard (see community above). This isn't turnkey, changing this means changing our minds first, our words and art, our laws and disagreeing with those that support revenge as justice.
Crime, non-forceful solutions;
4. The remaining motivation for using force, specifically firearms, to harm someone is generally financial gain. Robbery et al. I believe that ensuring that people's needs are taken care of will help with a lot of this. There is also greed. People who want more and would rather use force to take it, the work to earn it. This again becomes a social solution of de-empathizing conspicuous consumption, praising the inexpensive and functional, promoting people making their own art and aesthetic improvements.
Nothing is going to eliminate all crime, murder, suicide. But these changes will go a long way to reducing those root causes.