"If you expect a better world to come about from money, to come about from science, to come about from technology, that's wrong. If you really want a better world, a happier world, it ultimately depends on this: our hearts."

- HH The 14th Dalai Lama

Gun violence is just one symptom of a larger malady.
It comes in a package with racism, intolerance, injustice, insensitivity, hatred and greed.
Other symptoms ?
There's a mountain of trash floating around in the Pacific Ocean.  The polar ice caps are melting.  Antibiotics are losing their ability to fight disease.  Terrorism, despotism and poverty are all looming larger.
Clearly, if human society continues on its present path, we are doomed.
What should we do ?
There is no end of charitable causes to support.  We can pick and choose based on the goals of the organization and how well they spend our money.  Take a Look:

These are all noble causes.
But supporting one or another as the ultimate solution to our problems is just playing Whack-A-Mole.
What we really need to do is to take things personally.  Step up and take personal responsibility for what happens.

Dr. Martin Luther King Jr. put it this way: “If a man is called to be a street sweeper, he should sweep streets even as Michelangelo painted, or Beethoven composed music or Shakespeare wrote poetry. He should sweep streets so well that all the hosts of heaven and earth will pause to say, ‘Here lived a great street sweeper who did his job well'.  No work is insignificant. All labor that uplifts humanity has dignity and importance and should be undertaken with painstaking excellence.”

Whatever we need to motivate us to work to become our better selves, whether religion, science, meditation, exercise, joining a club, or taking a hike, we should do with gusto.  We need to take up our brooms, and sweep the streets of our mind.  When the paving stones of our mind are clean and shiny, we will see not only our own reflection, but the reflections of others.  We will be able to say with Walt Kelly, from his comic strip Pogo, “We have met the enemy, and he is us”.
We are the ones who have the potential to destroy ourselves and other living things.  We have created nuclear weapons, nerve gas, overpopulation, slavery, war, and famine.
These things can't just be wished away.  We can't argue them away. To make these terrors disappear, we need to clear our minds so that we can see them as they are: the exact consequences of unthinking and bad behavior.  We need to become aware of and take responsibility for each of  our actions so that we can learn to weigh the consequences in terms of good and bad.  If an action contributes to the good, it should be encouraged.  If an action contributes to the bad, it should be discouraged.  Replace bad thoughts with good ones at every opportunity.  Replace anger, with kindness.  Replace fear, with vigilance.  Replace the desire to do harm, with compassion.

But this is no easy task.  It requires constant attention.  We owe it to ourselves, and each other, to try.  And if we can manage it, the world will change.  Not because someone invented a flying car or a faster computer, but because we will have changed our hearts and minds.

Here's another (slightly paraphrased) quote from HH The 14th Dalai Lama: "If you think that nothing as small and insignificant as you are can make a BIG difference, try sleeping with a mosquito."