Before you decorate you should do a little cleansing to make sure that your space is free of negative energies. It means that you are creating a clean slate on which to decorate. There are several different traditional always for clearing a room of bad energies. It all depends on the culture or spirituality that you might be referencing as you cleanse the room of bad vibes.
For instance, in Feng Shui it is clutter that attracts bad spirits and blocks the positive flow of energy. If you feel haunted or overly attached to the past, one remedy might be to give your house a good cleaning. If the object feels wrong, or reminds you from the past in a negative way then throw it away.
Another way of keeping bad energies out of a room is to hang bells or chimes on the door. Every time the door is opened to the room the spirits will be frightened by the noise and be chased away.
Another way of clearing your space is to walk through it, ringing a bell that rings in the key of C. Balinese temple bells were created specifically for the purpose of getting rid of bad energies.
A Wiccan tradition for clearing vibrations out of a house is to take a broom and starting at the front door, sweep the entire house in a counterclockwise direction. Even if your floors are clean you can do this as a symbolic action. Keep sweeping in the counterclockwise direction until you have reached the front door and sweep everything collected out the front door and down your front path and to the street. Modernists could probably use a vacuum cleaner to the same effect.
In Celtic traditions and also Feng Shui traditions four copper pennies place in the North, South, East and West corners of the home are thought to prevent the inhabitants from astral attack, ghosts and spirits.
The classic incense used for protection from bad energies. is a combination of Frankincense and Myrrh, which is said to please the angels and summon protective light. Genuine Frankincense and Myrrh can be bought in religious supply stores and burned over charcoal in and incense burner. The burner is swung through the house, cleansing every corner of thought forms, entities and bad energy. In Arabic homes today, on Thursdays, frankincense is burnt in a censer and carried through the living rooms and bed- rooms to expel evil spirits and invite the angels in. In Cairo, Egypt, and elsewhere, people make earn the livelihood by travelling from business to business, burning this combination of incense to dispel any negative energy left behind by the public.
Sage can also be used to purify an environment. It can be bought commercially as stick incense or as a sage bundle. A bundle is usually just the dried herb wrapped with an elastic band or rope. The bundle is lit on fire and carried through the house to clear it of entities and bad spirits. In several Native American cultures, the aroma of burning sweet grass or sage purifies the energies and attracts the positive supernatural entities.