It would be a combination of laws that decrease the number of guns in circulation. As I keep repeating in these types of thread, look at Canada, Britain, Australia, NZ, comparable first world nations. The measures these countries have in place mean fewer guns in circulation and therefore fewer that fall 'out' of circulation and onto the black market.
The measures include, licenses, restricting certain types, enforcing certain bans and prohibitions, amnesties and buy backs - all sensible stuff. The results are simple - there are fewer guns around, even criminals find them harder and costlier to obtain, those who have a history of domestic violence or gang associations are shit outta luck and therefore fewer people as a percentage are harmed or killed by guns in those countries.
I know the NRA thinks licensing and the Second Amendment right are mutually exclusive but that's hogwash. You need the proper permits already to exercise that right in various manners all across the country: silencers, conceal carry, open carry, mag caps and fun switches, are all affected by various laws and permits here and there. So people still have the right as long as they can demonstrate the responsibility.