Reddit reviews The Practical Art of Divine Magic: Contemporary & Ancient Techniques of Theurgy

This book has instructions on it:

Patrick Dunn - The Practical Art of Divine Magic

One of the first exercises described:

\> EXERCISE 1.2: EXPERIENCING THE ONE

>This exercise is the complement of the previous exercise. Where in the previous exercise we explored the nature of matter through our imagination and found that apart from our senses it is at best a tenuous fog of possibility, in this exercise we will strive for an experience of the One. This isn’t an exercise you will succeed at immediately or find easy, and in many ways it is a constant practice you can and should undertake regularly, both to give yourself perspective and to continually strive for henosis. It is possible for us to experience the One as well as matter because we exist in every level of existence: we are bodies, minds, souls, and as such partake of the One itself. As Pauliina Remes puts it, “The fact that the human soul extends to as many, or almost as many, levels as the metaphysical hierarchy ensures that it has the cognitive and other powers suitable for the penetration of all these levels.” 2 The more work with theurgy you do, the easier a taste of the One will become.
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>I take this exercise from the Hermetica, where it is described like this:
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>Enlarge yourself to an unmeasurable size, leaping outfrom the whole body, and, having transcended time,become Eternity, and you will know the divine.Think that nothing is impossible to you; consideryourself to be immortal and able to understandeverything: all arts, all sciences, all the ways of life;become the highest of the heights, and the lowest ofthe depths. Gather together all the sense perceptionsof objects in yourself, of fire and water, dry and wet,and in the same way, be everywhere—in earth, insea, and in the heavens. Be not yet existing. Be inthe womb, newborn, old, dead, and that whichis after death. And understanding all such thingsthe same—time, place, events, qualities, quantities—then you will be able to know the divine.3
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>STEP 1: When first beginning this exercise, it helps to get as comfortable as you can. As you become familiar with it, you can do it while doing other things (although I wouldn’t recommend doing it while driving!).
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>STEP 2: Focus on your breath. Aim for a four-fold breath, where you inhale for a count of four, hold for a count of four, exhale for a count of four, and hold for a count of four. If you’re sitting still, with some practice you should be able to do this, but if you’re moving about you may find it easier to aim for a count of two rather than four or otherwise modify the time.
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>STEP 3: Imagine yourself from outside yourself, as if you have a floating-eye perspective of the scene. It is as if you are watching yourself sitting or lying there, like in a movie. You may close your eyes if you want.
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>STEP 4: Build up this image of yourself as accurately as you can. Then slowly begin to lift your perspective upward, taking in the room, then the building (assuming, of course, that you’re inside), then the city. With each breath, take in a bit more, and don’t be afraid to go slow. If you begin to lose focus, rest on that level of perspective for a while.
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>STEP 5: Eventually, you will take in the whole world, then the solar system, then the galaxy, then the whole universe as a whole. If you don’t manage this the first few times, don’t worry. You are gaining benefit just by seeing the big picture as high as you can.
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>STEP 6: When you can hold the universe in your imagination, contemplate the totality of it without focusing in or catching on any one thing for a few breaths.
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>STEP 7: Now, holding it all in your mind at once, let the boundaries between all its parts dissolve: the galaxy is the same as the people, and all perspectives collapse. If you can do this, you may glimpse a moment of unity.
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>STEP 8: If you can achieve step 7, which may take some time, try now to abolish even the boundary around the universe. The experience of this is hard to describe, but you will probably find your discursive, binary mind stopping in a sudden awareness of unity. This is a glimpse of henosis.
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>STEP 9: Whether you got to step 7 or not, after holding the image of the entire universe, or the oneness behind it, for a while start to move back inwards to the galaxy, solar system, planet, continent, and location. This helps ground the experience; in theurgy the return is as important as the journey.

I do not practice theurgy myself, so take my advice with a grain of salt. However, I do have an interest; although I'm still curious as to if it would fit with my other practices and belief.

I would recommend starting with this book...

The Practical Art of Divine Magic: Contemporary & Ancient Techniques of Theurgy

And perhaps considering this school...

http://www.thedivinescience.com/