Mayhaps your original vampire story? Or genuinely literally anything youd like to talk about
Oh boy, that thing is huge. It's one of those cases where there's a detailed society worldbuilding and characters and....not that much of a plot, heh. Well, no, actually there are three potential plots with several vaugely connected characters and it's a matter of which one wins out. So uhhh a bunch of worldbuilding stuff it is?
Eat Or Die. That's the first and foremost rule of the whole thing, in universe and out. Vampires consume human blood to live. Vampires must make a kill, at least one every four years. No exceptions. If you don't do this you will starve to death. Animal blood will come right back up, so will Starbucks, so will toast. You can share the same human to consume, and it still counts but at the end of the day, you can't continue unlife without death. The four year rule is the bare minimum and even that is pushing it; a kill every other year is a healthier minimum. The longer you go hungry, the more the body does what any hungry body does: it breaks down. And when the body realizes "hey we need to eat" it starts making executive decisions like when to eat. Or who to eat. The fact is an ethical vampire who just kills once every four years is far, far, FAR more dangerous than the vampire that makes a kill every month. Well fed vampires are vampires with control.
New vampires in denial who snap and devour their own family or significant other or children is so common it's considered a rite of passage in some communities.
Creating vampires, as far as anyone knows, cannot be done on purpose. The likelihood increases the older the vampire, and you are completely unable to turn anyone before your First 40 (the first 40 years of being undead) ends. It is theorized this is to stop population booms, or else a way of nature guaranteeing the only ones making more vampires are those who can take care of them. If you make it through the first 40 years you probably know what you're doing.
It's not exactly "forbidden" to turn someone and ditch them (vampiric society is still relatively new and there are few hard and fast Rules) but it is very frowned upon. Somewhere around the late 19th century vampires became more social, and in the shadow of the Civil War, many saw the benefit of staying together. It's also a good way to stace off loneliness, and everyone remembered how lonely and scary it is to change all by yourself. The practice of sticking around to care for your "begotten" had always been around, but those who did it were considered softhearted wierdos.
There are two groups of vampires: tangles and knots. A tangle can be applied to anything between a general group of vampires to a gang to a bloodline. (Though one could argue a bloodline and a gang is the same thing) The word comes from the slang word, as in to fight, because for years the only reason more than three vampires would be in the same five mile radius would be to be a territorial fight. A knot is closer, tighter, harder to separate. A group ranging from two to six vampires who are close and care about each other to some degree. There can be multiple knots in a tangle, or a knot can be solo. Kill part of someone's tangle and they might ignore it. Kill part of someone's knot and you're going to have trouble.
Vampires--at least in America--are and always have been extremely territorial. They have to be, because blood is a finite resource and keeping under the radar of the living is always a delicate balance. To enter someone's territory you MUST be invited. You are allowed to pass through without one if you're traveling but you must keep moving. No poaching, no stealing, or else.
Territories are broadly split into six quarters in the United States: The Northeast, Southeast, Southwest, and Northwest are exactly what they sound like. The Wild Midwest stretches in one solid line down the middle of the country where vampires live under no authority or leader, and where none can impose it. There are still knots and tangles, but they're in constant flux. It's where those banished from the broader territories often run to.
The sixth major territory is The Little Civil Kingdom, aka New York City. The boroughs are individually run by vampires with fancy titles (The Baron of Brooklyn, The Prince of Cony Island, etc.) and ultimately ruled by The King. They are constantly at war with each other in a cramped territory. Basically Gangs Of New York Meets The Warriors But It's Vampires. It technically should be part of the Northeast but that would mean all off The Kingdom calling a truce to fight whoever in the Northeast made such a dumbass decision and The Kingdom will almost certainly win because it's been Like That since there was a New York. They are the meanest and fiercest of the broad undead territories.
The Southeast is generally agreed upon as being the second meanest. Like The Kingdom, it's from overpopulation and also probably because the heat angers the blood some.
Vampires can't cross running water. (Streams, creeks, rivers, etc. Swamps are fine, oceans are not. Manmade doesn't count, so no you can't just dig a moat.) Rivers are theorized to be why the big territories are drawn as they are, but nobody knows for sure.
Vampires don't burn in the sun. However, they do lose virtually all of their vampire powers. Not decomposing counts as a power. It gets worse the older you get. Someone dead for a year will only feel like garbage. Someone dead for fifty years will smell like a rotting corpse because that's essentially what they are. Also will severely hurt their eyes without sunglasses.
Silver hurts and kills. A wooden stake I'll too, but it's not the stake itself so much as death from starvation. It makes one completely unable to move, so either someone helps you or you get to die slow. Decapitation works too but difficult to pull off. The easiest method is fire. Fire always works.
The best way to keep a vampire from devouring you is to tell them your name and that you have a family. Vampires stick humans into two categories: people and food. If you don't want to be food, be people. They don't like to eat people. It makes them feel weird. You will likely still die (it's a security risk, you know they're a vampire after all) but you won't be fed upon. Probably.
Herbivores do not like vampires. At all. It is difficult for a vampire to ride in a horse drawn carriage without the horses losing their minds, and riding a horse is out of the question. Notably, social structure of the undead began to solidify when trains became popular. You would think the automobile would do the same, but many vampires don't know how to drive.
After the First 40 it becomes increasingly difficult to change or adapt or learn. It's possible but very difficult. Not unlike ghosts, they default to the time they died in and the majority of human history moved much slower. The 20th century jumping from telegraps to internet in under a century is something everyone originally born before 1950 is still reeling from.
Aside from some rare exceptions, vampires don't have that much money. They work in a barter system (food, sometimes services) and if they have jobs they still work paycheck to paycheck. Banks are suspect, partly because they're a potential paper trail and mostly because of the Great Depression. If they have money it's mostly in cash. Part of the reason for tangles under a leader is that leader might have a house to sleep in, or money for a hotel. Or they've made a begotten who does.
Vampires don't have money because most of them never had any to start with. You feed on whoever isn't going to be missed or made a fuss of. Therefore, the safest target are those with little money, or in a demographic the authorities don't care about. Vampires, again, aren't created on purpose and are a roll of the dice. Whoever is preyed upon becomes the broad population of vampires eventually.
Vampires aren't exactly immortal. After about 250 years or so, they experience what's called "the unraveling" which, for brevity's sake, is something like vampiric dementia. It can be staved off by being active, keeping the mind busy, and eating well. However, even doing everything right, someone that old will start confusing years, cultural norms, forgetting names, and what the current laws are. It's not unheard of for a 300 year old vampire to walk out their door and be hit by a car because they don't know what a car is. It is also not uncommon for a vampire that old to instantly fall to dust and bones because, just for a moment, they forgot what the sun can do.