An aggressive promotion, expansion, and funding of mental health services, funded by taxpayers.
Expansion of social services in general, esp. those centered around troubled/high-risk youth.
The immediate cessation of valorizing anti-intellectualism and the willful promotion of contempt of education.
Gun control laws that at the very least make it more difficult to acquire firearms, for everyone. Severe penalties for lawful gun owners who do not properly secure their firearms and which are later used to commit murder as a result. Mandatory registration, licensing, and training, subject to yearly re-certification.
Stop romanticizing guns in our entertainment, in much the same way smoking was.
These are off the top of my head. They are NOT ironclad, they ARE subject to change, they are NOT exclusive, and they are NOT a one and done solution. So please don't make like I'm suggesting they are in your response.