I would be a naughty ghost. Not a mean one, just a naughty one. I would howl and laugh and cry and sneeze and cough and make whatever other sounds to frighten people when they’re alone in the middle of the night. Where did that hiccup come from? Is it a ghost? Yes, ‘tis I, the thing that goes burp in the night!
Now, these other things depend on if ghosts can touch physical objects or not. If so, I would poke people. Mess up their carefully crafted hairdos. I would open the creakiest doors I can find, move objects around, open and close curtains. While they’re in the bathroom, I’d change the placement of their silverware and cups and plates when they were eating, and when they return, they’ll think, “I could’ve sworn my cup was to the left of my plate….” I would also take a stuffed animal or figurine or something and place it all over the house. They move the shower curtain, and it’s in the bathtub. They open their car door, and it’s buckled in the front passenger seat. Or maybe it’s seated at the dining room table or nestled in their bed.
Sometimes, I would be a nice ghost. They would return to find their laundry folded, spices alphabetized, dishwasher emptied. Of course, they would panic and wonder who broke into their house and wrote out the bills, but still. That’s to make up for giving them nightmares at night.
A Spectral Duck