I want to write a fiction book that centres around the supernatural and the occult. Tips?

You will want to read extensively in the field, both traditional and contemporary novels, everything from the Malleus Maleficarum to Blatty and Koontz and Yarbro and Clegg.

talk to someone who is a Wiccan, because they are considered “occult” by established religions
and then the question posed to you is how are you planning on writing this? because the whole occult spirit guiding thing is become a little cliche

Cliches come up when there is not enough conflict, the road from beginning to end is too smooth. Make sure your stakes are high enough, also make sure your characters have some flaws and quirks. I recommend the below book, I was able to borrow it from my local library, it gets you to focus on making your writing stand out regardless of genre.

Engross yourself as much as you can, read about it, watch about it, listen about it. Use a thesaurus and if you have an character go insane then stay in isolation for a few years, I had to stay in isolation for some “issues” and I basically ended up going insane. It really does help a lot in writing about it. Though it isn’t a pleasant experience.

You need a good set of characters and a strong plot first. Your interest in the occult will certainly provide colour but cannot replace the above or the ability to write well.

Do a lot of research. Wicca is a religion that you will want to research. The four winds and the guardians would be a place to start. The witch’s bible is available at most book stores that have a ‘new age’ section. Also you will want to make sure you understand the symbols and the difference between a pentacle and a pentagram. Remember for every force there is an opposite force. For good there must be evil, for light there must be dark. For the living there must be dead. ect.
Now you must decided from which angle you are going to use? Are you going to go with the established religions ideals that witches are bad? If you are going to go that route I would also speak with a member of the clergy to understand what they see as inherantly evil.
Being a wiccan myself, there are alot of challenges that us memembers of the ‘occult’ are faced with, not unlike any other misunderstood religion. For me, Wicca is more of a lifestyle rather than a religion.
I would do as much research as possible on everything that you plan on including in your story. Talk to a witch, or a meduim. Talk with someone who has had a spiritual experiance. Spirits can be many things. The dead that have passed, souls that were never born or other things- creatures, demons, or just cross deminsional creatures that can’t find their way back to their own world.

Everything is so over done in this genre, that it’s all cliched now (and still gets published) so don’t worry about it.
However may I suggest you try something with more of a tinge of reality, read more “factual” books on the matter, what people really believe/d and centre the story around real superstition and actual belief.
You say your involved in the occult, so write a novel based on that, on your experiences of the field, and exaggerate it into being possessed or using spells to your own means (you have to put in some cliches as these, or it will turn off the reader)