A well regulated militia being necessary to the security of a free state, the right of the people to keep and bear arms shall not be infringed.* See Disclaimers Below
Short version: everyone who bears arms does so in the name of the state and should be subject to military discipline. Easy.
It is a difficult sentence to parse. It's also very controversial. Some argue that this is a collective right retained by the states to form militias—something with, quite frankly, confederate valences. Others argue this is a personal right meaning Congress can't stop people from having guns.
Whatever your knowledge of U.S. history may be, you can't really understand this right based on our history alone. Going back centuries, "bearing arms" was a noble prerogative. Having arms, or being "armigerous," meant, among other things that you had a heraldric emblem. In most of Europe, "bearing arms" meant you had been granted arms—i.e. a heraldic logo—by the authorities, and were part of the nobility. (My favorite one is the Scottish Lord Lyon King. Simba!!) In England, having arms made you part of the gentry at least, even if you weren't "noble."
This was, among other reasons, associated with nobility because arms were expensive. But also because arming the peasantry (or the villeins) could have bad consequences for the noble classes.
And certainly this bill was influenced, as was most of the Constitution, by the Whig movement arising after the English Civil War. The English Bill of Rights prevented the king from interfering with people having arms. (Guns? Well, guns weren't synonymous—1 Henry VII 1508 required letters patent to have a gun.)
Now, without getting to muddled in the details, both the English and American Bills of Rights were meant to keep meddling sovereigns out of common law rights. So, for example, King James II or King George III—or, as some feared, the federal government. Subsequently, most of the American Bill of Rights has been deemed to apply to the states as well.
Now, I could comment on how the American bourgeoisie wanted to ape the English nobility a lot—especially in the South—and wanted to do everything they did. But maybe I'm getting a bit too psychological there. (Or Marxist.)
Regardless of whether it's a collective or an individual right, it's a right that is intended to be used in a "well regulated militia."
To use the metaphors of the past, then, I would suggest that if you choose to bear arms, you are voluntarily joining a militia, even if it is a militia of one (pun intended). In order to be well regulated, you should have to comply with military discipline.
To me, that means if you are using a gun (or a long sword for that matter) in the commission of a crime, you should be subject to a Court Martial, perhaps at the state level. (California has a State Military Reserve that is sort of the reserve for the National Guard—maybe you should be compelled to become part of that.)
For me, gun ownership isn't about defending my home from burglars. That's what the police are for. It isn't about killing animals (not kosher). It's about perhaps restoring order in the event of a disaster or some kind of civil breakdown. (I live near a nuclear power plant, near an earthquake fault, and where a tsunami could hit, among other reasons.) For that reason, I have no problem keeping my guns locked up, far from their ammo (literally buried) and never think about it.
If all of these guys want to play dress up soldier, well, shit man, they should have to take on those responsibilities too.
* I am no libertarian. Under their oversimplified and polemical framework, I am a "statist." Also, I have zero problems with the current restrictions on gun laws. I can wait 10 fucking days and let them do a background check. Most crimes are committed with handguns not assault weapons, but I also don't care about the bans. So what.