The Demons of the Ars Goetia are Fomori, First Children of the Great Goddess… not unlike many devils and other diabolic beings from our world’s mythology. See Creation Myth. They are an embodiment of chaos, exiled to other worlds, bound in shadow, fire, and darkness. They seek toeholds into our world, harboring a desire to one day regain all they have lost. To this end, they are more than willing to answer a summoning and enter into pacts with the Third Children… mortal men. (The enemy of my enemy is my friend.)
They can give much, but they often require much. Only the foolish will attempt to summon them without something of value to give in return. Aleister Nacht stated it simply and beautifully: “Success comes from win-win situations and your ability to align yourself with the wants of others.” This legal concept of quid pro quo is “truth” when it comes to working with Lesser Powers, and will contribute to unimaginable success in your workings. Be prepared to till the fields and sow great quantities of seed if you wish to reap a great harvest though. If you are lazy, unimaginative, and are unwilling to put some hard work into your craft, more likely than not all you will end up with is a handful of weeds.
Various sources will prescribe certain observations or requirements for rituals specific to certain demons or classification of demons. I find very few of these hold value. I agree with observation of the age of the moon, primarily 2, 4, 6, 8, 10, 12, or 14 days old being the best nights to summon. The requirements for the seals to be cast in metals have no inherent value. Beautifully crafted drawings are equally effective. The old seals themselves are very powerful. Colors used for inscriptions should be to the taste of the witch, don’t get hung up on this. Ensure you wear a pentagram around your neck. A simple necklace will suffice. Have a wet towel with you inside your circle, to be used to cover your face as protection against the sulfurous and flaming breath of the demon you summon. Have a brass vessel and lead plug available if you intend on containing a demon. I do not recommend attempting this… particularly with one of these 72 demons. Additional seals and incantations are required, which will not be explained at this time. You have been warned. Some profess a need to fast or practice abstinence for a period of time before attempting one of these rituals. Garbage… Go screw, lick, and eat to your heart’s content beforehand. Indulge… it will give you power and you will be less distracted. A final note in this regard is the old curses for demons that will not come forth and obey. Do not engage in them. If the subject of your summoning does not appear, try again another night. If your pact is not accepted, come back another time with a better offer. Honey catches many more flies…
A word of caution; Summoning or invoking these demons can put one at odds with the Sidhe, particularly the Seelie court. They are vigilant against the return of the Fomori… and their servants. Remember, these demons hold no love for mankind. Their gifts come at a price… and their desire is destruction of all we know. Use caution and think with a level head. The power you can potentially gain does not have words to describe adequately.
Familiarize yourself with Evoking and Summoning. Insure that the seal of the demon you are summoning is inscribed, along with your other arcane formulas, within all three open spaces in your thaumaturgic triangle. I will post a picture of each seal for your use.