There clearly isn’t a perfect solution, but I’d probably start with federal single payer healthcare that allows all Americans to have easy access to mental healthcare. This would solve a lot of other issues not related to gun violence as well. At a state and local level we should increase mental health access in schools, perhaps with a full time mental health professional on staff for some schools or districts.
Let’s treat guns like cars. In order to own a gun you must pass certain safety courses and obtain a license, you then must register you guns annually and you must own insurance on them to cover any accident. Then lets regulate the guns themselves. Let’s focus especially on hand guns and put a strict limit on the amount of rounds a gun can hold and limit the number of guns that are produced and sold so that, gradually, the volume of guns in the country decreases. There’s probably other things we could regulate on guns that I don’t even know about, I think the goal should be to make it really, really hard for an individual person to shoot a high number of people in a short period of time.
Nothing’s perfect, nothing is going to be a quick or easy fix, nothing’s going to be fool proof. But just because we can’t “stop” tragedies doesn’t mean we can’t or shouldn’t try to significantly reduce them, if we truly believe that life is valuable and should be protected in any meaningful way.