I would require military service as a prerequisite to gun ownership. I know this would never happen, but I think it is very reasonable.
It would guarantee proper training.
Guns were originally intended for a well organized militia, so it makes sense that gun owners at least served in the well organized professional military at one point in their lives.
Avid gun owners usually claim to be great patriots, so spending some time in the miltary should not be a problem for them.
There would be no shortage of service people ever.