My good friend, seminary professor and theologian, Gerry Breshears, has written/compiled three different articles related to this subject. He has done extensive research and has firsthand experience in dealing with demon possession.
Three Models of Deliverance (from demon possessions)
Deliverance Ministry, addressing issues such as demonic deliverance
Basic principles for dealing with the demonic
Also, see the article “How should a Christian respond to mental illness?” There are several resources listed there.