I think the best solution would be to repeal the 2nd amendment and just take the guns off the street. That's not happening in my lifetime, though, so I think we should set gun control policy based upon the facts of previous mass shootings.
1. Most school shootings are perpetrated by students. You should have to be 21 to own or use a firearm of any kind. There are too many kids who are not mentally ready to hold life and death in their hands.
2. Gun owners should be required to lock their guns in a heavy duty safe that cannot be removed from their property. If your gun is used to commit a murder, you should face a charge similar to murder yourself. Keeping your combination or key from your kids is your responsibility.
3. The gun tax is a good idea.
4. You should not be able to have a gun that fires more than 6 shots in a single clip. Also, no automatic or semi-automatic weapons.
As long as guns exist, there will be gun-related violence. I think there is a lot that can be done to curb that violence, though.