Answer:
To have a proper seance it is important to have a reputable medium to conduct it.
The medium will have a set of instructions and requirements of his/her own. The best mediums do not need darkened rooms, candle light, or spooky music, those sorts of things are more common in fictional reports or with unethical practitioners.
I do not recommenced the inexperienced try to do this sort of thing on their own as there are some fairly nasty things that can happen.