You can always say guns don't kill people, people do. But do we really need automatic weapons sold to citizens? I know in Australia after the Port Arthur Massacre there was a near complete ban on all semi-automatic rifles and shotguns, and all pump-action shotguns.
Make it harder to get weapons and don't allow such powerful and quick to fire weapons to be sold to citizens. That can be the first step.
EDIT: Just read some of the slack laws they have over there:
http://www.news.com.au/story/0,23599,21576049-2,00.html 
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