In the Golden Dawn one mainly thinks of Divination as Geomancy, Astrology, and the Tarot.
“Divination” itself is an ancient concept – and it is only by going back to see what ancient sources said on the subject that one gets to realise how important it really is. One of the most important authorities was an ancient adept known as Iamblichus, who lived in the third and fourth centuries AD, and who wrote an enormously influential work known as “Theurgy, or on the mysteries of the Egyptians.” He was a neo-Platonist: he also admitted to being influenced by the Hermetica, and his writings have influenced the whole Western Mystery Tradition, including the Golden Dawn.
This is what Iamblichus had to say about the subject:
First, then, thou askest that it shall be explained to thee in detail what it is that takes place in the prognosticating of the future. It is impossible to set forth at once what thou art trying to learn. For according to the gist of the question, thou imaginest something like this of the art of prognosticating: as that it is generated, and something existing in the realm of nature. But it is not one of the things that are generated, nor what a certain natural mutation accomplishes, nor some ingenious product which has been invented for useful purposes in everyday life − nor, in short, is it a human accomplishment at all, but divine, and beyond the realm of nature; and having been sent down from the heaven above, unbegotten and eternal, it naturally takes the first place.
“Divine, and beyond the realm of nature” – that is in fact why we call it “Divination” – because what we are really trying to do is not just discover the future, but to discover what is the Will of the Divine in any given situation.
In other words: when you draw up an astrological chart – your first thought should be not that you are looking at an arbitrary arrangement of stars and planets – you are in fact reading off a message sent to you from the Creator of the cosmos. When you draw a tarot card, you are not looking at a piece of cardboard with some pretty pictures, but at a communication from the universe to yourself. And most importantly – when you experience the spark of intuition which unlocks the inner meaning of a tarot spread or astrological chart or geomantic figure, it is not just some psychological process involving the interaction of your conscious and unconscious minds, it is in fact the Divine Will itself speaking to you.
True Divination, therefore, is what turns magic into Theurgy. For example: say you have an idea to cast a spell, or consecrate a talisman for some purpose. What you should do is always perform a Divination beforehand, asking “Is this a good idea?” And often it is the case that a Divination will actually say “No, it’s not a good idea,” or “It will bring about unforeseen consequences,” or even: “It will bring about consequences which you probably could have foreseen if you were brutally honest with yourself.” And so based on that you modify your original intention in light of the Divination, or even abandon it altogether. It can go against your ego, and be a bother, but it has to be done. When you make your magical practice align with the Divine Will through divination, you are entering into a harmonious relationship with the universe. If however you ignore Divination and just go ahead regardless, you are doing nothing better than sorcery, and probably attracting a whole load of unpleasant karmic effects upon yourself.
So: always do Divination with the intention of trying to discover the will of the Divine – not mere fortune telling. Treat it like a divine science – regard your tarot cards and the charts you draw up as sacred objects, if it helps you reinforce these concepts. And when you discern a message coming to you from your efforts at divination, treat it with the respect it deserves and do not ignore it.