A famous magickal device is a witch bottle. Fill a glass jar with nails, pins, razors, shards, stones, etc. Invoke power, charge it, and declare that it is a protector against negativity. Cap the jar and seal with wax or rubber cement. You can bury it near the porch or hide it in a dark place.
Witch bottles work for one to five years.
Image light streaming from the bristles, and aim it around the room, invoking hallowing power. Placing a broom upside-down against the door is an old spell to bar negativity from entering. Malignant force thrives in filth and grime. Cleanliness thwarts negativity. Poltergeists are often the effect of a female teenager who is enduring stress.