The Paranormal Investigator Book 1: Practical Spiritual Tools is a great tool to have in any investigation kit. It gives simple examples on how to protect oneself before, during, and after an investigation.
"I feel it is important to say that this work, paranormal investigation, is not to be taken lightly. When opening yourself up to the paranormal unseen world it is vital to have some ground rules for protection of yourself and others, " Christia Cummings-Slack