It also makes you resemble Mr. T, and nobody wants to join a religion he belongs to. Citronella candles may not be used in rituals. I cannot stress this enough. Pastel colored candles in the shape of cute animals are like direct sunlight to the Powers of Darkness. If the spirit contacted during a seance begins offering financial advice, you're dealing with a con artist, and not a genuine medium.
Flourescent lighting is very annoying to most netherworldly creatures.
When the Black Mass goes awry, stay away from the Evil Priest. Enraged demons always go for the pompous. Followers who have a speech impediment should be excused from speaking parts in any and all ceremonies. The mispronunciation of the deity's name can have catastrophic effects. Plan ahead by selecting ceremonial robes that are easy to run in while still affording ample concealment.