For one, if you look at the types of firearms, in Germany you will find extremely few in the "self defence" or "assault rifle" category, mostly they are in the "hunting" or "marksmanship" categories.

Then you have safe gun storage, which is mandatory in Germany and is subject to routine inspections.

It is also mandatory to have an ownership license for any type of gun. You will be automatically denied this e.g. if you are formerly convicted of a serious crime, have mental health issues, or a history with drug use or violence. And you need to provide a reason for owning a gun, where "self defence" does not count.

If you can prohibit people from owning guns made for killing lots of other people, and prohibit people who obviously should not own guns from getting them, you've made substantial progress.