People are often disconnected because there was a disconnect in their childhood. You can go fully gory with the abuse, but you don’t need to (no need for rape, locked in the basement on the weekends, or Father beat her with a belt every time she sneezed). Absent parents or parental figures is a good way to create this disconnect. Having parents that are not only absent, but have only had hyper critical interactions with the character could be good. Instead of having an info dump with the MC explaining their parents are never there, just don’t feature the parents at all until the MC has a friend over. When the friend observes that the MC’s parents aren’t at home, the MC can comment that they aren’t ever at home and elaborate a little further on when the subject is brought up. Finally, when the parents are at home, have them be superficially nice to the MC before they tear her down with some comment.
~~Example: MC just ran through the woods to avoid a predator or monster. and enters the house to see her mother is there in the kitchen. Mother happily greets the MC and MC breathlessly returns greeting. After a sort, way to polite conversation (the sort strangers might have with one another, not mother and daughter), the mother will ask why it is that the MC’s hair is always so ratty…completely oblivious to the fact that the MC just avoided death. The MC doesn’t elaborate because there’s no point. She knows her mother won’t believe her, nor will she probably do anything about it.
A lack of connection will make general caring a mystery to her. She might know what friends are, but unless she’s had any REALLY friends who’ve explained that her parents not being there is completely a form of abuse, she won’t know how to immediately form any connections with others that aren’t completely shallow and just polite. Throw her in a new town and give her people that actually care? She’ll be mind blown even without the vampires!
Now, creating attractive characteristics in an emotionless person is a bit trickier. Being pretty is something that plenty of people are, so we got to find her something that will actually make people want to go to her house and check in on her, not just be seen at school with. HOWEVER, it’s the type of personality you want her to have that will ultimately decide what that attractive quality is.
~Is she a good girl? Maybe she’s a genuinely good person, but the lack of connection has stunted that fully blooming. She sees someone trip, she helps them up and moves on before they can say thank you. Someone can’t pay for their groceries and she happens to have the right amount of cash on her (maybe the only cash on her) she’ll pay without being asked and move on before they can object. Other people that actually understand social interactions will pick up on this fast and will gravitate toward her - good and bad. Good people will want to be around other good people. Bad people will want to take advantage of an easy target.
~Maybe she’s naturally a bit wild. Maybe she’s got a penchant for causing mischief, she’s highly intelligent and observant. Because her parents don’t care and technically didn’t raise her, these traits come off as being a bit of a troublemaker. She claps back at teachers if they get the wrong answer, she’s more than happy to saying something witty under her breath and talk circles around people when they try to argue with her. She doesn’t care when people get mad at her because, hey, negativity is the only interaction she’s ever got at home. People gravitate toward that sort as well, especially if the girl is good looking. The MC is pretty, highly intelligent, and is fearless enough to no care about other’s issues? Those are the triade of a position of power, and plenty will want to be around that. Maybe her friends are the first ones that are gentle enough to tell her she doesn’t have to be so rough with others, that it’s okay to be vulnerable and let other’s issues roll off of her instead of snapping back.
Find out what kind of personality you want your MC to have…or let the reader decide!
Vampires are pretty simple. If you’re going to immortal bloodsucker route, then you really only have a few types of night dwellers. They can be anywhere from a new vamp to a thousand years old, but no matter what’s there, personality wise it’s pretty much just these, so don’t be afraid of being ‘cliche’. There’s NO SUCH THING as being cliche if it has your own spin on it. 
You got the type that loooove being a vampire because they are afraid of dying or have enough of a sadistic streak that sucking blood is quite enjoyable for them. They were probably jerks as humans or weak Peter Pettigrew type men that wanted something to set them apart. You could have this as you vamp and he learns to be less of a dick through his interactions with the MC, just as she learns to melt that ice queen venere that’s containing whatever is underneath. He might not totally change, but at least he’s less of a monster and gains some of that humanity he didn’t have as a human.
Then you got the tortured soul who didn’t have much of a choice in turning into a vampire, doesn’t like sucking blood, and is generally going to be a wet blanket for the rest of eternity. He doesn’t want to hunt. He doesn’t want to interact with others, and don’t you dare ask about being turned into a vampire, because he’s not going to do that to you…and if he has to, he’s going to be pretty miserable about it. Unless he specifically learns through some magic that he NEEDED to live a hundred years longer to met the MC, the love of his life or his soulmate, he’s never going to let go of that black cloud hanging over him. I’m looking at you, Edward Cullen.
Backstories aren’t too important with the vampires. All you have to say is he was a viking or a pirate or, IDK, a Mr. Darcy Lite and that’s enough. What’s more important is what in his backstory give him a connection with the MC? You could go the soulmate or true love route. Maybe he’s always had dreams of this one girl, but doesn’t realize it’s her until later on - like he’s dreamed over and over of this girl standing alone, waiting for someone on the side of a road, and in the dream, he can never get to her. And then he sees her, and it’s the MC, and hey! Maybe the MC is the key to solving his one big mystery from his past…maybe he’s been searching his entire life for what happened to his (father/mother/fortune/twin brother/arch rival) and the MC is the first hint he’s gotten in X long toward that. She’s wearing the same family crest as his rival - now they have ot figure out why she has it. She’s got the sam unique eyes as the man he saw taking his mother. She’s been sketching the face of his (slightly more sexy and charming) brother in the margrins of her notes! Have fun with it, butgive him a reason he needs to be all up in her buisness!!!
if anyone could help me out with some original backstories that would be much help.