There can't be just one thing that'll help reduce crime. Here's 3 answers that WILL reduce it:
Discipline- Everything starts at home, and parents have to be willing to tell their kids at an early age 'no' and apply corrections when necessary. Spanking, taking away toys/electronics, time out, no TV/Computer/Smartphone/Tablet/Movies, all this is letting them know that their actions that are bad have consequences. Maybe reestablish a form of it at school, just in case.
Education (so, yeah, the first choice would be one I'd select)- Like discipline described above, but learning why certain things are bad is very important. Learning about the law and how it applies to everyone, including kids is a good way to make them understand. Even show the benefits of when good actions. And if it's guns, teach kids (and adults for that matter) they have to learn about safety and interacting with a firearm. That'll solve a lot of your gun problems right there. Just saying "we're going to ban all guns" or something to that affect will not help in solving these problems because they will still happen.
Parenting- Being a parent, instead of a kid's best friend, goes a long way. The point of being a parent is to help raise your kids to not just help them grow, learn to defend themselves, and to make them more independent, but to also to correct them whenever they do something they're not suppose to. Don't abuse the children, but just enough to where they will learn their lesson. Lastly, it's to help them to understand that they have to yield to authority, and parents are the authority when raising their kids. If those kids don't learn to respect their own parents, they will not respect anyone else.
Education, discipline, and parenting all go hand in hand, and, in my honest opinion, THE 3 most important areas that MUST be acquired. Those 3 alone will prevent a ton of crime. But there are other areas that are important such as mental health and influence. However, the first 3 are the top requirements. As far as laws, on the weapon crime front, just getting rid of or slapping more regulations on guns and knives doesn't solve the problem. We can use examples like Australia all day, but I will bet there's still a ton of gun and/or knife violence in place like that and their media isn't reporting on it. There's not much you can do with any new theft laws to lower its numbers. Assaults, trespassing, rape, and whatever else is going to occur, no matter what laws are put in. I'm glad there's laws and penalties for those terrible things, I'll be the first to admit that (gives a sense of security), but without proper education, discipline, and parenting, crime will not be reduced because people will try to find ways around them if they go unchecked in those areas. In any case, all this has to be accomplished at home. You do all that, crime will drop.