Practice the correct pronunciation of your deity's name in the privacy of your own room before chanting it in public. Flash cards are often helpful. Before agreeing to impregnation by a supernatural being, investigate the survival rate of the other people who have undergone the procedure. Citronella candles may not be used in rituals. I cannot stress this strongly enough.
Fluorescent 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. Thousands of cult members could be saved every year if they followed this simple safety tip. Contrary to historical belief, drugs and invocations do not mix. When the ritual goes awry, it is vitally necessary to be able to discern between the gibbering monstrosity to pump full of silver bullets and the gibbering monstrosity that will fade away after a few hours, some B-complex, and a good, hot bath.