Sage the place from top to bottom and surround it in a ring of blessed salt. You can also try hanging a protective sign over the door or drawing one in oil on the windows. Firmly tell the spirit to leave.
Do not attempt to communicate with it. You're opening up a line of communication you don't want, you just want it out if it is in fact an evil entity to begin with. It may not be "evil" at all.
Possession is not as common as all that.
(And the movie is actually based on the life of a woman named Anneliese Michel and what was happened very differently from the movie.)