The gist of it is that these kids don't value life. They don't value theirs and they don't value others. If they had something to keep them going and we had public programs available specifically for people that experienced heavy bullying, have few friends, have fallen behind on the social spectrum, have any sort of mental disorder, addictions to drugs or gaming, or even just feel like they want to talk to someone. There could be some sort of regular social event that can help those people that are outcasts find a place to fit in. Give them something to live for.
This should help on the first end of the shooting problem by lowering the number of socially isolated people, next you're also going to want to limit the media's ability to release the shooter's name and other identifiers.