One of the main things that should be discussed when it comes to the paranormal... DON'T INVITE THEM THROUGH!  Or in... or to be seen... 

Since the spiritual world is one of infinite unknown energy, it responds to energy being spent towards it more than anything else. If it feels like you're trying to get ahold of something on the other side... well, there's no telling what's answering your call.  So don't open that door!!