What are the rules and regulations vampires should follow?
There are two different kinds of "rules" to be considered. One is the set of "hard" rules that any soul-seeking entity has to follow, and the other is the set of "social" rules in the vampire community.
The first set of rules appear to be unbreakable. These are rules which, despite their effort, vampires, demons, and the like cannot bypass. I lump in demons and other dark spirits here because the rules are the same for both. Why exactly this is the case is not known for sure, but I have a very strong feeling that there are rules when it comes to the spirit world that even these beings cannot violate.
These spiritual rules seem to follow the idea that one cannot lose one's soul against their will. Vampires are those who have (in most cases) willfully traded in their souls for eternal life and power. The possible exception is the human who is unwillingly turned into a vampire (click here for more on this). Demons strive to take souls using fear and trickery, and vampires are essentially "authorized dealers" of this same trade. This is why these rules exist - to protect the innocent from losing their souls.
Another key spiritual rule is that vampires (and other dark spirits in physical form) cannot enter a "claimed space" without permission. This is most typically mentioned as being the home, but encounters with black eyed beings indicate that cars share the same status of ownership. Should the human leave the claimed space, it's fair game (which is why it's a bad idea to run out of the house or car if one of these beings is threatening you.) It's also fair game if you invite them in. An invitation can be revoked later, but a single invitation is considered "open until specifically revoked", meaning that these beings can come and go as they please once invited.
These are the two main, unbreakable rules for vampires. The other "rules" are more like guidelines that keep their behavior in check.
Like any community, vampires have an unofficial "social contract". Every community in the animal kingdom has some sort of way of keeping its members in line, whether it is through physical submission, exile from the group, or even shame or loss of status. Vampires are no different, especially because at one time every vampire has been human, and therefore has most likely already experienced social conditioning.
Also like any animal community, the biggest violation of the "rules", spoken or unspoken, is when a member of the group puts other members of the group in danger. Not just physical danger, mind you, but danger of losing power, respect, or ownership rights as well. For vampires, a lot of the rules that applied as humans go out the window, as they are now irrelevant, but the big concepts remain.
Vampires are very much a secret society. Even though every other novel today has vampires going to high school, in reality if these being really exist they are going to stay hidden away, making appearances among humanity only when there is little chance of being discovered and usually only when necessary to feed. Secrecy is key to any secret society (obviously), and vampires are no exception. It is widely believed that revealing the existence of vampires to humanity is one of the biggest violations. This makes sense, as it is a near certainty that if humans found out that predators were living nearby they would try to exterminate them as quickly as possible. Staying hidden as legends only protects all vampires from being revealed, which in turn keeps the group from danger.
Another big rule is that vampires are supposed to take responsibility for their "children" (i.e. humans that they turn into vampires). This is mostly for the same reason as above - a rogue vampire, unaware of the rules of their new society, is highly likely to attract unwanted attention and thus put the group in danger. It is also accepted (as it is in human nature) that those who "birth" the child are expected to raise them. To raise a vampire means to teach it its limitations (such as staying out of the sunlight) as well as how to hunt, how to charm humans, and how to stay out of trouble. New vampires are inexplicably "tied" to their makers as well, meaning they have difficulty being away from them for too long. This trait, which eases over time, has undoubtedly evolved for this social reason.
The only other big rule is that vampires are never to kill other vampires. Consequences seem to vary for each individual case (as they do in human life), but it is considered to be punishable by death (destruction).
Other than that, basic social manners should be followed. In such a small community one does not want to be disliked or cast out, so it is best for most vampires to live in harmony with one another as much as possible.
The rest of a vampire's limitations aren't really rules or regulations, but rather the same kind of "don't hurt yourself" basics that all creatures automatically try to abide by. Don't go out in direct sunlight, don't drink dead blood, don't set yourself on fire, etc.
I'm sure there are other rules, but I'm pretty sure you'd have to be a member of the society to know them all, and if you did, you wouldn't be able to tell anyone without risking your (second) life.