Vampire material: General vampire RP guide. Some points applicable to all.

[Sam Akabara]

First and foremost:
One of the hard lessons of Roleplaying is that it is not our characters strengths that make them interesting and fun. It is their weaknesses.

The Call of the blood:

So you're a vampire. A creature who feeds on the blood of others, who stalks the night, prowling for victims. That's great.
How the hell do you get into character?
In most games, you have something in common with your character. But what do you have in common with a vampire? They don't even breathe. So how can you really feel you're part of this character, how can you make it your own?
Well, you both eat to survive. That's something in common.
You eat burgers, they drink blood. And now you're roleplaying as one. How weird is that? It's not like you can call the local blood bank and order a pint of AB negative to go, either. You have to hunt for your food, and then you have to devour it, usually live. Definitely not a character for the squeamish.
But, how do you get used to that concept?
Try remembering the last time you were really hungry. I mean REALLY hungry- Not just peckish or nibbly, but that time you forgot to eat for two days and your stomach felt like it was going to rip right through your flesh and devour the nearest passerby.
Remember that? The Light-headedness, the shaky hands, the sharp pangs that almost doubled you over? The way your tongue felt thick in your mouth and your saliva flowed at the mere mention of food? The way the smell of break baking or donuts could make you dizzy? Focus on that hunger, that's vampires feel every time they need to feed. It's a real addiction for them- the blood is what keeps them vital. Without their fix, their bodies will lock up, cease functioning and return to the death they are merely forestalling. But that won't happen easily, it's not like a vampire who hates his existence can simply refuse to drink and die quietly. The instinct to survive is strong, stronger in them than it is in us. After all, they've survived death itself. Even if a vampire consciously decides not to eat, his body will still hunger, and eventually its reflexes will take over. That's something you may have experienced yourself, but to a lesser degree. Someone puts some pizza down in a box to share. You know you shouldn't but you find your hand reaching out and grabbing one anyway. That's instinct, and the vampires’ reflexive attack is much the same thing. It's just its more intense and dangerous.
In other words, you can think of your characters appetite in one of two ways, either your vampire feeds reflexively or does so consciously. If it's the former, you don't have to worry about it too much. The vampires body takes control when it's hungry, no need to think. The beast takes over when it's hungry and goes for food. Whether the vampire blacks out and wakes up to find their mouth bloody and their hunger sated or stays conscious but passive the entire time like a passenger on a roller coaster is up to you. Of course, you'll need to decide how your character feels about these feeding frenzies. Does he simply accept them as an unavoidable price for continued existence and ignore them? Does he bemoan them and hate the fact that his body refuses to quit? Or does he keep trying to ameliorate them-Placing himself in the middle of a farm, for example, so he only feeds on cattle, or breaking into a prison so that only criminals die at his hands? It's up to you how much control your character has over his hunger, the longer he waits before feeding; the more likely his system will take control and leave him to reap the consequences. Whatever the case, you'll probably be watching that self-control dwindle away, and Humanity will likely follow.
Some vampires don't wait until their bodies react. They take the initiative and feed willingly. If that's what your character is like, you need to think about his thought processes. How can he accept the notion that others must die for him to live? Does he refuse to kill, and only take a little blood from each Victim? That may reduce the guilt, but it takes a lot longer to be sated and increases the risk of being caught or interrupted while feeding, as well as increasing the frequency with which they will have to feed. Some vamps are picky eaters. They'll only take cops, or redheads, or college students, or whatever their victim of choice is. Others will attack anyone. These creatures may seem more savage, but they're simply being practical. Blood is blood, after all.
If your character feeds willingly, ask yourself about his dining habits. Just as some insist on using a fork and knife, and others will only eat on paper plates, the vampires have peculiarities and preferences on their food. Does your vampire need the chase to work up an appetite? Does he prefer to strike suddenly, to cause as little pain as possible? Does he only feed on the homeless and the crazy, as no one will believe their tales?
Simply put. Think about how your character can tolerate killing. How do they cope with it?
Principles:

Vampires are immortal. While they can be killed, they do not die of old age or from natural causes. They need no food such as humans eat, and they do not need to breath.

Vampires are monsters: True and false. Vampires are not monsters in the sense of "Oh, look, a scary demon" but a combination of tragic factors draw them toward wicked deeds. Newly created vampires think and act much as they did in mortal life. They do not immediately turn into evil, sadistic monsters. However, the vampire soon discovers their overpowering hunger for blood, and realizes that their existence depends on feeding on human beings. In many ways, the vampire’s mind-set changes - they adopt a set of attitudes less suited to a communal omnivore and more befitting a solitary predator.
At first, most are reluctant to kill, the vampire however is finally forced into murder by circumstance or need- and killing becomes easier as the years pass. Realizing that they, themselves are untrustworthy, they cease to trust others. Realizing that they are different, they wall themselves away from the mortal world. Realizing that their existence depends on secrecy and control, they become a manipulative user of the first order. And things only degenerate as the years turn into decades and then centuries, and the vampire kills over and over, and see the people they loved age and die. Human life, so short and cheap in comparison to theirs, becomes of less and less value, until the mortal "herd" around them mean no more to them than a swarm of annoying insects. Vampire elders are among the most jaded, unfeeling and paranoid 0 in short, monstrous - beings the world has ever known.

Ghoul: Avoid use of the word ghoul as a verb. It's awkward and met gamey and just plain odd in a weird, vaguely unsettling way. Kind of like using Shatner as a verb. Just say no.

...Serve the clan...: What's your last name? Do you serve your family? What's your nationality? Do you server your nation? No, you're just a person. That's what your clan is - it's just another characteristic. Note that this phrase is applicable in a select few cases, such as Justicars severing the Camarilla, Templars occasionally serving their bishops, etc., but you do not (generally) serve your clan unless you have attained some sort of rank within it that demands an according service.
It happens a little in the Assamites, somewhat in the Giovanni. Most often in the Tremere, but even that is a relative statement.

Principles
remember that being a vampire is a curse.
Vampires feed on the living and contain a turgid beast. No one is "Rewarded" with the Embrace unless it's a back-handed reward, intended to be as much punishment as prize. Only the most bizarre or twister individual actually wants the Embrace- Unless that character has an imperfect understanding of what a vampire is.
Remember that the Disciplines are just that, not super powers. They're supernatural abilities of a predator race, not laser blasts from a superhero's electro-fists.

Think through your characters motivations. Characters need to be....Well, characters, and not cardboard cut-outs or plot devices. Trickster characters, for example, don't just hop around and "Cause chaos." they need to have a purpose for the actions they undertake.

Bear in mind that survival is issue number one. Vampires need blood. Vampires need to hide from a mortal world that would destroy them if it knew vampires existed. Vampires need contact with others of their kind, for they are egotistical creatures and need to feel that they are vital to the unlives of others. Everything else is a creature comfort.

Go ahead and be a Drama queen. It's the end of the world when a Ventrue slights a Toreador, or when a Nosferatu dares to steal a Tremere’s magic trinket. For all their glamorous veneers, most vampires are little more than arrested adolescents. As vampirism "freezes" ones physical development. So does it freeze their emotional development as well? Vampires don't usually become any more "Mature" than they are when they're Embraced.

Be Stylish. Survival may be issue number one, but looking cool while doing it is issue number two. If you don't look cool, no one will respect you. And if no one respects you, you're going to have a hard time at Elysium.
On the other hand, don't be florid. Stylish is one thing, but overwrought ruins the effect. It's not cool if we know you're trying to be cool.

Noncombat conflicts and methods are more important than fighting. Combat results in getting hurt or getting killed - most people go out of their way not to get punched in the face. Vampires potentially have forever lain out before them. Are they going to want to risk it by getting in gunfights and sword duels? Combat should be singular and dramatic, not yet another panel of this month’s action comic.
There's always something bigger and badder than you out there, and vampires who constantly pick fights are going to encounter bigger, badder things far more quickly than vampires who don't go knocking on deaths door.

Vampires ride history, they don't guide it. It's okay to have a vampire who'd profited from the industrial revolution but your character did not cause the industrial revolution.
To that end, heed the mortals. Six billion of them out there, after all. Remember the Masquerade, as well.

Know when drama becomes more important than maintaining the hidden world. You may feel limited by much of this, but that's to make it all the more dramatic when something comes down the pipe that really needs to be dramatic. I'm not saying you can't have a gunfight, I’m saying that if every night is a pitched battle through the streets of L.A. with SWAT teams and helicopters, you'll lose much of the sublime nature we're trying to create.

Don't resort to rude or pithy comedy. Being a person who subsists on the warm blood of his former fellows is a terrifying realization and condition. Don't have your character joke about their fate. It's not funny, it's horrific.

Don't make your characters Tom Clancy protagonists. So a character can use a rifle- there's no need to make him a Navy SEAL. RP should be scary because it casts the mundane in a sinister light. Your neighbor could be a vampire, and fear comes from the fact that you wouldn't know and his proximity. Exploding ninja Bruce Willis vampires spouting one-liners before decapitating a dozen IRA loons with their three-bladed Katanas are out of place.

Don't overestimate the use of supernatural power. Given his druthers, a vampire would prefer to enact their schemes without drawing attention to the fact that something otherworldly is at work.
Dominate a person into giving you money, that’s going to attract attention if handing you money is out of character for that individual. If you blackmail him, well, that at least won't be creating any Masquerade breaches. Remember most disciplines require a coin to work. They're not guaranteed effective.

Don't be WAHOO! Action is thrilling, but uses it to punctuate an RP story or illustrate a theme instead of using it for its own sake. You may wish to use some WAHOO! Because monotony is boring. But make it worthwhile. This is not a modern dungeon crawl or wuxia film.