The 2nd amendment has two parts to it: 1) the RIGHT to keep and bear arms and 2) the RESPONSIBILITY of a well regulated militia.
People should not be able to just go out and buy a weapon without ALSO having some sort of training and instruction. The institution of a national firearm's license would require that people undergo some sort of safety course and pass a test (much like a driver's test) to receive their license. As with all licenses, this one can expire meaning that people will have to renew and be able to demonstrate adequate safety skills.
a license such as this could be required anytime a person wishes to buy a firearm or ammunition.
As opposed to banning weapons, this could greatly reduce accidents and negligent discharges.