There's no simple way to really do it but if you take away all the guns the folks who are doing shootings will consider other means of taking life. Probably more extreme rather than less. It's not a gun issue. It's a responsibility and mental health issue. It takes a village to raise proper healthy minded individuals and there's science to prove it.
Children who are not brought up favorable conditions tend to have issues. And no that doesn't just mean poor financially. Rich kids have it too.
A big thing would be for everyone to have proper access to Healthy Nutritional food while being able to also access clean/safe housing and education.
There's a few folks in the world who have the finances to do things and pay people to do them without going broke but their spaceship buttplugs are so far up their asses it's putting a load on their brains.