Make it personal. According to Horror Factor, nothing makes a story scarier than drawing on your own personal fear. If you have a fear of the dark, for instance, try writing a spooky story set in the middle of the night during a power outage. By drawing on your own emotions, you'll be able to convey the spookiness of the situation more strongly and effectively. Even if your readers don't share the phobia, your own sense of fear should shine right through the words on the page.
Choose your villains and monsters carefully. There are plenty of traditional spooks who show up in stories: ghosts, witches, vampires and werewolves. According to Writinghood, if you choose a traditional villain or monster for your spooky story, try to add a new and original twist, to keep your readers guessing. It's also possible to invent an entirely new ghoul, or maybe to choose a villain who isn't a monster at all. For instance, could the next-door neighbor be hiding dark secrets?
Create strong, realistic and likable protagonists. Especially in a spooky story, which may have supernatural or unrealistic elements, it's important for your readers to identify with the main character. If scary things happen to the character, maybe they'll happen to the reader too! According to Horror Factor, when readers are rooting for a character, it will make the plot much more suspenseful. Keep your characters believable and grounded in order to enhance the spookiness taking place around them.
Avoid easy or happy endings. This depends on personal preference, but some of the spookiest stories usually involve an unhappy ending. This will leave readers with a final scary image that they'll remember for a long time. According to Writinghood, the ending is one of the best places to include an original and unexpected plot twist and really make the spooky story your own individual masterpiece. If you can't help having a happy ending, you can still try to make it a little spooky, to leave readers wondering what happens next.