Here are the Rules of Gun Safety as posted at the Fill Yer Hands zombie-proof bunker in Kennesaw, Georgia:
0. Always wear eye protection, and hearing protection where warranted.
1. All guns are always loaded.
2. Never let the muzzle cover anything which you are not willing to destroy.
3. Keep your finger OFF the trigger until your sights are on the target.
4. Always be sure of your target and what’s behind it.
5. Never try to catch a dropped gun.
All these rules apply to Nerf and Airsoft and BB guns, too, for a couple of good reasons. First, these guns can hurt you if you don't follow the rules, and second, if you don't follow the rules with these guns, you're likely to ignore them with "real" guns, too.
This sign is posted at the Nerf Gun / Airsoft storage area in the zombie-proof bunker:
Rule Zero: Eyes and Ears.
We also store the eyewear in the same place as the ammo for these guns. It makes it a lot easier to remember.
When we are at the range, the first thing we do after setting up targets is go over these rules with everyone in our party. Everyone there knows they are free to call any of the others on a rule infraction. This isn't meant to be mean, it's meant to keep everyone safe.
Usually, Rules 2 and 3 are the ones to violated, but usually only once. All I have to do is yell "Muzzle!" or "Finger!" and the person gets what I'm saying.
I find that with my son's friends, one of the hardest things to teach is to point their guns at the ground when not shooting, not in the air. Thanks a lot, Hollywood.
It makes me feel good when I pull into the driveway in the evening, and my son is leading an assault on his backyard action shooting range, and he and the four teens with him, all armed with Airsoft or Nerf guns, are all wearing eye protection. In fact, my son has on knee pads and shooting gloves.
I am more than willing to furnish eyewear for all the shooters. And I am more than willing to banish someone who refuses to wear them.
I recently came across this video from the NSSF that explains the Four Basic Rules very well.