First, you can use spooky instruments like the theremin which has an otherworldly sound. Then, add in some low, deep tones to create a sense of unease. For example, a slow - paced, deep bass line can mimic the feeling of something lurking in the dark.
For me, the soundtrack of 'It' in 2017 was excellent. The music added a lot of horror and mystery to the ghost story. The combination of creepy sounds and intense melodies really enhanced the overall experience.
Ambience is crucial. A cold, damp - like soundscape can set the mood. And dissonant melodies. They create a feeling of unease. For instance, chords that don't quite fit together in a traditional way can make the listener feel that something is 'off' in the ghost story world.
A good soundtrack for a ghost story should have elements like eerie melodies. For example, slow, minor-key tunes can create a sense of unease. Sounds of creaking doors, howling winds, and faint whispers can also be added to enhance the spooky atmosphere.