For starters, a well-regulated militia would include:
Every gun owner must take federally mandated training, tailored to the gun they own, includes mental health check. Must repeat every 2 years
30 day waiting period on new gun purchases
Private gun sales must go through federal broker, also subject to 30 day waiting period
Ban clips larger than 10, confiscate anything larger
Limit ammo purchases everywhere except shooting ranges. Can rent larger clips at the shooting range. Cannot take ammo or large clips from shooting ranges home with you
Raise minimum age of gun ownership to 21
Must carry gun insurance. Insurance company financially liable for any crime committed with said gun
Gun owners are criminally liable if their gun is used in a crime, or accidental shooting by a child, and they are shown to have not properly protected it (locked in safe for example)
Ban military-style protective armor