Based on 3e Ravenloft:
- Most things are normal and harmless.
- The bad and scary stuff likes to lurk in the background and/or hide in the shadows.
- Nightfall is typically the point when the villain(s) gain and hold the advantage; similarly the heroes have the advantage during daytime.
- The villain can be destroyed by exploiting his weakness - IF you can find out what it is. Of course he keeps such knowledge hidden, a deep dark secret - and slays those who find out before they can tell others.
- A rare soul will learn the secrets of power, not for himself, but to protect the Innocent from the power-hungry. When you meet one such, treasure the experience and try to keep him alive; he will come up with the esoteric knowledge you need to complete your quest, usually at the moment you least expect it.
- Great heroes and great villains have a story dominated by the power of emotions.
- Good and Evil both exist, there are shades of grey but the moral slope heads towards the extremes not the middle.
- The traditional gods do not answer prayers in a visible manner. They may be the still small voice that pierces the silence, but most often a person is on his own to make moral judgments / decisions.
Read some classic horror stories, and have your PCs do so as well: Mary Shelly "Frankenstein's Monster", Bram Stoker's "Dracula", Edgar Allan Poe's "The Raven". "The Fall of the House of Usher". Original "The Phantom of the Opera" (not the musical). Do this to help get into the mood.
Watch the black-and-white movie versions of Dracula, Frankenstein, and The Wolfman.
Borrow the 3e Ravenloft guide from the library and look through it for inspiration.