We all know what a ghost is, right?  It is the part of a dead person that refuses to leave earth for some reason.  The part remaining might be the dead person's unfulfilled soul.  It could be more shallow characteristics of the person that composed their personality.  Maybe what is stuck is the aura that used to surround the body but now floats around, groundless.   

In one form or another, this apparition is stuck and most likely doesn't understand that its body is no longer sensing and is in fact, buried or even cremated.  Oftne they don't know they are dead because they did not have time to prepare for death.  These are not the people who died after a long bout with cancer.  These are the Dead Like Me deaths that were freakish or emotional and certainly unexpected. 

Ghosts often have unfinished business to complete, which makes them inspiring material for storytellers.

To create a compelling ghost story, a writer must understand what it is this particular ghost wants. Realistically, a ghost wants to stop being a ghost, and go on its merry way towards a better life. Especially if the ghostly part left behind is the soul. Souls embody a person's deepest spiritual nature, so if you are telling the story of a soul ghost, righting a wrong might be what it needs to move it along down death row.  Or protecting a loved one until they can accept this person's death.  Or something pretty compassionate.  A soul ghost generally does not get stuck without a compelling reason.

For ghostly personalities, it is a whole different experience. Personality ghosts may dwell on revenge and other shallow thoughts. If you are considering writing a series, personality ghosts might be good candidates, because they don't want to leave earth as much as they want to throw tantrums and make life miserable for others by haunting them, etc. These are the types of ghosts who disappear by means of ghostbusters. These ghosts are not good protagonists. They make better supporting characters.

Ghosts who are merely auras must transcend the color chakra where they are stuck. This means somehow they must learn something and change. But they might not know they need to learn something. They might think they are just fine as they are. So they don't really know what they want. They need to be taught what they must do to move on to another reality. These ghosts can be very very stubborn and egotistical, but in the end, they leave readers changed and satisfied.

Stories do not evolve around ghosts alone.  There must be compelling characters surrounding them.  And each of these characters must want their own stuff.  Plots come alive when characters want opposing things. 

Like, in the book Evermore by Alyson Noel, everyone in Ever Bloom's family dies in a car accident but Ever.  And Ever's little sister Riley, now a ghost, refuses to leave her sister.  Ever wants her to stick around because Riley is all the family she has left.  But there is a small window of opportunity for Riley; if she doesn't join her parents in the spirit world soon, she will be doomed to hang around earth forever.  Yet, Riley knows her sister needs her AND she is living her high school life vicariously through Ever.  This builds tension, as the reader is torn.

Characters were invented to carry storylines even though the storylines originate from within characters.  It's all circular.  But characters who do not carry the storyline can be eliminated by considering whether they advance the plot or not.  Perhaps they carry a portion of the plot and then their usefulness is finished.  These are the characters that have unfortunate accidents, the ones evil ghosts might send into traffic, the one who dies to perhaps rise again with new qualities that further the storyline. 

You decide.  You are the author. 

Some ghost stories are silly, like Eva Ibbotson's Dial A Ghost, where a temp agency hires out ghosts. Of course the plot thickens when the agency mixes up the order and sends a nice family of ghosts who died when their home burned down to an evil household that wants them to frighten their nephew to death. Talk about feeling inadequate!

Generally, however, ghost stories are meant to send chills down reader's backs, so think of what scares you and write scenes that raise your hackles as well as your readers. Throw in a few eerie settings, but keep away from fog and dark alleys. They are dead giveaways. Something along the lines of a haunted mall escalator or ice cream store might create unexpected horror.

Be sure to balance out the tension so that your readers can break for lunch. A steady diet of fear does not a story make. Speaking of lunch, add in sights, sounds, tastes, touches and smells that contribute to the tension as if it was happening outside on the lawn.  The more details, the better.

And end each chapter on a page turner... with a question the reader MUST have answered or they will put the book down and forget to pick it up.

Accomplish this much and viola! You are a ghost writer!