I'm assuming that the haunting is because I had a vendetta against the haunted. In that case, I'd make their life miserable in the most subtle ways, including but not limited to:
Move their furniture half an inch at random so they keep stubbing their toes.
Make their clothing get stuck in doorhandles.
Loosen the knobs on their drawers.
Loosen the screws on the handles of their pots and pans by an eight of a turn.
Shift things in their cupboards so that something falls out every time they open them.
Damage the gaskets on their windows so that there's a draft and constant whistling sound.
Reopen their resealable packages a little bit so the food spoils faster.
Make their toilet leak, but only when they're sleeping.
Pack lint into their phone's charging port so that their charger never plugs in snugly.
Unbalance their appliances so they rattle/shake.
Slightly unbalance their car tires.
Loosen fasteners in their car so it produces annoying rattles.
I would press the reset button of the modem constantly. Also disconnect the phone charger at night but connect it before they wake up so for some reason it only charged about 5%
The toilet leaking seems like a little too much effort for me, but otherwise I'm on board. Don't forget moving their small and easily misplaceable objects when they set them down. Maybe just around the room a little bit, like putting their phone on their seat when they get up instead of the arm of the chair where they left it.
Demand to know "are we there yet?" while haunting their house. Because of your going to haunt somebody and scare them, you might as well confuse the hell out of them too.
Convince some kid that they have to spend a considerable amount of their lives, dedicated to figuring out why I'm here, and how they can figure out how to help me 'cross over'.
Then after a year or two I'd just get bored and tell them I made all of that up, and this is pretty much it. Then I'll go possess some guy to play videogames I guess.