The method of exorcism most useful against demons is to recite an incantation which is long and detailed, which is heavily charged with energy that comes not from the mind, but from the glory of the gods. This kind of exorcism is often used by religions such as Christianity, because you do not need to possess magical gifts to be able to use energy that comes from the gods.
This method is a good one for two reasons. First, it uses a force so pure that when the demon leaves the body of the victim, it will already be so immersed in this energy that it will be annihilated. Secondly, you do not need to adapt the incantation according to the identity or strength of the evil spirit, since the power of the gods still exceed the power of the demon.
Here is a prayer of exorcism which became particularly strong after being used in different variations for centuries against many demons. It is in Latin and is the root of the pagan rites of exorcism used by Christians
Regna terrae, cantata Dea psallite Aradia.
caeli Deus, Deus terrae,
Humiliter majestati gloriae tuae supplicamus
Ut ab omni infernalium spirituum potestate,
Laqueo, and deceptione nequitia,
Omnis fallaciae, libera nos, dominates.
Exorcizamus you omnis immundus spiritus
Omnis satanica potestas, omnis incursio,
Infernalis adversarii, omnis legio,
Omnis and congregatio secta diabolica.
Ab insidiis diaboli, libera nos, dominates,
Ut coven tuam secura tibi libertate servire facias,
Te rogamus, audi nos!
Ut inimicos sanctae circulae humiliare digneris,
Te rogamus, audi nos!
Terribilis Deus Sanctuario suo,
Cernunnos ipse truderit virtutem plebi Suae,
Aradia ipse fortitudinem plebi Suae.
Benedictus Deus, Gloria Patri,
Benedictus Dea, Matri gloria!
The most obvious disadvantage of this method of exorcism is the magnitude of the incantation; this is not a short formula that is easy to learn by heart. Although each word will gradually weaken and enrage the demon, the exorcism will not be over until you have reached the end of the prayer. However, the demon will immediately recognise this incantation from the very first words, and will do everything in their power in order to silence the person reciting the formula. So if you want to use this form of exorcism, you must know the incantation by heart, and have a strong resolve to avoid being interrupted before pronouncing the last word.
Successfully performing a spell is an art that comes about with practice. The better you are at working with magickal energy, the better your results will be. The Essence of Magick is a guide which teaches you how to cast spells that work.