The Law of Invitation is the one that is most invoked in cases of Demonic activity.  This is where to one degree or another someone denounces there allegiance to God and pledges there's to Satan.  In one form on another.  Using a Oujia board is a great way to conjure a demon into your life.  Using trance mediums are another way of conjuring up demons.  Sylvia Browne is a prime example of this and I will go into greater detail later on.  These things are called Necromancers and Soothsayers.  Any type of fortune telling is a mortal sin.  Just understand that what is politically correct and considered tolerant are in many ways paths to hell.  Occult practice in any form can open the door to the demonic and can in essence lead you to being attacked.  You can also invite a demon inadvertently.  Even the simple act of damning God, can invite an entity into your life.  Another common way of inviting a demon into your life is by accepting it.  If you are experiencing a haunting in your home, and you decide that it is something you are going to accept, then if it is demonic you have given it permission to infest and continue to get stronger.  Your acceptance and show of attention can fuel it's energy.