The Player, to be The Player in this role-play means to simply respond to the plotlines given to you. This is not as easy as simply being in battle or responding to a character. This means knowing your character, not simply starting with a profile of the bare basics and going from there. The most successful Role-Players here have spent a half-hour or more thinking of and making a character.
Think of the person, how they react. It will do if the character is yourself, as long the character CHANGES as the Role-Play goes on. That's another key to horror Role-Play, the changing of characters. If your character lives long enough to become powerful, that should show, in most a pyschical nature and a mental one. The things the characters are faced with daily are enough to plummet many humans into insanity. Reflect that. Many characters here were once human, and either spiralled into insanity and then became something no longer human, or were well on their way before they met the main characters.
Another important thing to remember: Badasses are NOT supposed to be your main goal in creating a character. Witty, sharp, brutal, sure. But not badass, not powerful for the simple sake of having a powerful character. This undermines the whole idea of HORROR, which is, at the roots, humans who are against forces they don't understand and can't defeat.
Respond to the Keeper as your character would, no attempts to be badass or cool, simply act as your character would.
The Keeper is the harder of the two roles to fulfill, for it requires the ability to adapt quickly and adjust well laid plans depending on how a character or a group of characters reacts to their plots. Therefore, the role of The Keeper is not suited for everyone on this site, while others might find it remarkably easy. There are many components to being the Keeper that must come together to make a successful plotline.
Ask the admins about ANY plotline beforehand.
First off, make a being that is both threatening and interesting. Yes, a giant, all-consuming Darkness is threatening, but not interesting. Give the being a reason or a backstory that not only justifies their power, but makes them beings of pity, fear, or other emotions that may be applicable.
Also, don't make a plotline for the sheer sake of making one of your own characters powerful or killing off a character you dislike. That is not interesting at all, that is simply abusing whatever permissions the Admins have given you for that character. Also, the Keeper CANNOT exclude someone from a plotline simply because they think that character would tip the scales or "ruin" the plotline for some reason.