Let’s say that ghosts are spirits of the dead. (I’m not saying that they are or aren’t. I’m taking the question at face value.)
Think of them as people without physical form in our plane. They’ll behave the same as the living… more or less, anyway.
Tip: Many ghosts can be sorted into one of three categories:
1. Benevolent spirits who are simply revisiting our plane. (“Casper” ghosts.)
2. Ghosts with a story to tell before crossing over, or some task to complete. (They’re the “unfinished business” ghosts.)
3. Petulant/obnoxious ghosts that act like two-year-olds in need of a nap. (I’m often reminded of Beetlejuice, the movie.)
In general, consider what might interest a living person, and cause him or her to approach you.
Don’t treat ghosts as if they’re aliens, hard of hearing, slow-witted, dangerous, or performers.
Some ghosts are shy. Others have been taunted (or “provoked”) in the past. Be patient.
Many ghosts courageously approach investigators and establish rapport. Then, those investigators leave and never return. Often, the investigators didn’t even say goodbye. Remember, ghosts have feelings, too. Treat each ghost with the same respect you’d treat a living person.
Some ghosts quietly observe you before making themselves known. It helps to wait quietly for 20 minutes before investigating any location. The ghosts have time to get used to you.
Other ghosts might respond to specific stimuli. That could include a trigger related to the ghost’s death and later hauntings. Or, you could try a trigger from happier moments in the ghost’s past.
Theater ghosts are different. Usually, they respond well to direction. Politely tell the ghost what you would like him or her to do.
You may need to explain how to communicate with you. For example, you could tell him (or her) to knock once for yes and twice for no, or to speak through a device or an app.
Before investigating well-known haunts, learn what’s been successful at that location. It may work for you, too.
If you’re at a new location, experiment. Trial-and-error works. Take a variety of investigation tools with you, or plan enough visits to establish rapport with whatever is there.