In the olden days, what was incredibly hard about even starting a career as an Occultist was finding decent books to study. You had to go searching in dusty old bookstores, poring through libraries' "Special Collections" sections, and snatching up those few rare books that some major publisher might choose to print. And if you didn't live in a big city, it was almost impossible to get anything at all.
And by "olden days", I don't mean the 19th century; I mean the 1990s. Up until very recently, if you were interested in the occult you had to put up with only having access to a tiny number of titles.
But today, the problem is just the opposite. If you want to, you can download 30000 occult books to your tablet. All of the classics are being reprinted, and every would-be Dr.Strange out there is writing a manual. The 'occult' section on Amazon grows by hundreds of titles a week... and 90% of it is utter crap. The problem isn't getting the books, it's knowing what's worth getting! So, here's a very brief and totally incomplete guide of where to start:
First up, a couple of the really fundamental guides to western wizardry.
1. The Magick of Aleister Crowley
By Lon Milo Duquette (one of the most readable occult writers alive today), "The Magick of Aleister Crowley" was previously published as "The Magick of Thelema". It's a beginners guide to the system of magic developed in the 20th Century by Aleister Crowley, the western system of magic organized for the modern age. Here you'll learn the basics, including the fundamental rituals and exercises of a magician.
2. The Chicken Qabalah of Rabbi Lamed Ben Clifford
Also by Lon Duquette, this book is the best-written 'beginner's guide' to the Qabalah, the system of Jewish mysticism. But this is the Hermetic version of the Qabalah, not the one Orthodox Jews practice and not the one Madonna and other Hollywood new-agers are into. It's taken out of its religious Hebrew context and redesigned into a more universal system of understanding and contemplating reality. The Hermetic Qabalah is like the 'road map' of most modern western systems of magic, the basic atlas of what occultism is about and how it explains the universe. If you don't learn at least a little Qabalah, you won't have any idea what you're really doing when you try to do magic. Luckily, "Rabbi Lamed Ben Clifford" explains these very complex mystical and cosmological concepts in a ridiculously easy (and very funny) way that lets anyone figure it out!
Once you have the basics, the next thing you'll need to do is learn a lot about occult symbolism and correspondences (what symbols are connected to other types of symbols). As well as how numbers connect to words, and what objects, incenses, foods, etc., connect to different kinds of spiritual forces. This is important, because it's like the 'programming language' of western magick. It's how you get wizardry to work.
3. 777 and Other Qabalistic Writings
This is the great early compendium of modern magical correspondences, all organized through a series of tables, structured around the Qabalah. By itself, it does nothing, but when you are learning how to put a ritual together, this is the manual you need in order to know what materials to use.
4. The Magician's Companion
Bill Whitcomb's "the Magician's Companion" is another collection, a kind of 'magical encyclopedia'. It presents a huge glossary of all kinds of symbols from various western (and a couple of eastern) occult systems, as well as a big list of gods and their historical attributes, and loads of other stuff. It's incredibly useful for quick reference, especially if you are still in the learning process. It's also probably the best book on this list to get if you're not really interested in being a practicing magician, but just want to learn a bit more about occult ideas and symbolism.
5. Godwin's Cabalistic Encyclopedia
It's called an "encyclopedia", but Godwin's book is more like a huge dictionary. An essential part of interpreting magic, especially things like magical visions or revelations, is from a process in the Cabala called "Gematria". This is a secret code connecting numbers to words. Through it you can find links between different concepts. So if the number '250' corresponds to The South, Noon, Prosperity, a Lamp, a shout, and rejoicing, it means all the ideas contained in these words connect to each other at a mystical level (and thus, at a ritual level). This is the sort of stuff that leads occultists to great spiritual breakthroughs, or just drives them insane. There's a smaller version of the same sort of stuff in 777, but Godwin's is a much bigger and more complete source.
It's not enough to just read about occult symbols. You also need to learn how to use these symbols in an applied fashion. Divination systems are used for this. They're thought of by most people as 'fortune telling' but their deeper occult purpose is not (just) to tell the future, but to ask questions to further understand yourself through the 'language' of symbols.
You can also use them as 'flash cards' for the Occult. Because they're freed from the confines of a 'book' form, you can work with them to train yourself to get much more familiar with occult symbols, which will be really useful for you later, in performing magic.
6. The Thoth Deck
The Tarot has long been connected to the occult, but there's one particular deck that's just a powerhouse of occult imagery: the Thoth Tarot. Created by Aleister Crowley and Lady Freida Harris in the early 1940s, it is a startling artistic and symbolic masterpiece. Its art is incredibly psychedelic for the era, and still stands out today (even in a market with literally thousands of tarot decks). If you pick it up, it's strongly recommended you also get Aleister Crowley's "The Book of Thoth", one of the best books on the occult structure of the Tarot ever written. It is a very dense book, and you can't expect to understand it in a single reading. If you find it way too hard, there's also a Lon Milo Duquette book about this to simplify things for you: "Understanding Aleister Crowley's Thoth Tarot".
7. The I Ching
The I Ching is one of the oldest books in continuous use in world history (dating back to over 3000 years ago). Unlike the tarot, which was on the sidelines of European history, the I Ching is one of the central books of Chinese culture (one of the "Five Classics", the fundamental books of Chinese intellectual thought). It's not just a system of fortune telling, it's also a complex guide to mathematical cosmology and a philosophy of self transformation. It's easy to start using, but it takes a lifetime to decipher its mysteries. A lot of western occultists (including Aleister Crowley) used it more and thought it more profound than the Tarot.
8. The Runes
The third great system of occult divination are the runes, the magical alphabet of the ancient Vikings and other northern European peoples. Each rune has its own set of magical, mystical and symbolic imagery, and runes have their own entire system of magic. You can buy pre-made sets of runes, but more hardcore occultists often prefer to carve their own. It's more "legit"! If you do buy runes, don't get cheesy crystal runes. Or, Odin forbid, cheap sets on plastic or ceramic tiles! Traditionally, magical runes are meant to be carved on wood. If you want to be especially old-school, you should use Ash wood. There are lots of books on the runes, some of them awful, but quite a few that are good. I'd particularly recommend the work of Edred Thorrson or Kveldulf Gundarsson.
9. The Inner Sky
Only a few modern magicians use Astrology to try to 'tell the future'. But almost all occultists study astrological symbolism for magical purposes. So it's important to understand the system of western astrology, which is connected to ritual magic, talismanic magic, and alchemy. Most books on astrology are absolutely godawful drivel. But there are some exceptions. One of the best beginner's books on astrology for this type of understanding is "The Inner Sky", by Steven Forrest. Of course, if you aren't sick of Crowley by now, there's also his more advanced book, "General Principles of Astrology".
So all the stuff we covered so far are just the very basics. Now, the core of it all: the books that will help you turn all that knowledge into making yourself a serious occultist.
10. Magick: Book Four (Magick In Theory and Practice)
"Magick: Book Four", also popularly known as "Magick in Theory and Practice" is the magnum opus of Aleister Crowley's work. It's a gigantic tome, with the modern (complete) edition coming in at about 900 pages. It includes a whole guide to magical philosophy, occult holy books, the practices of serious old-school yoga, and to the theories and foundations of magical work. It also has a huge appendix full of rituals. If there was a single 'desert island' book for a magician to have, this one would be it. Of course, if you can't use it to get yourself off that desert island, you wouldn't be using it right.
11. Magick without Tears
The one thing you can't get in "Magick In Theory and Practice" is an easy read. It's got everything, except simple down-home advice on how to be a great occultist. That's where Magick Without Tears comes in. It was the last book Crowley ever wrote. It was also by far the easiest one to read. It was actually a collection of letters from Crowley to one of his students, and it has a homey/friendly kind of style that was totally different from Crowley's earlier writings. With this book, you get the practical side of the practice of magic.
Trippy Advanced Stuff
OK, so here's where it gets weird. Well, weirder. You have all you need by now, but there's some more hardcore magical work that is thought of as being for different levels of 'advanced' occultists. Which of course means that most total newbies rush to these books like flies. Then they get surprised when nothing happens, or when they get all messed up from it. Start with the basics. Build up a discipline of fundamental exercises. And once you've gotten really good at the stuff in all the books above, then try some of the advanced work. Not before.
12. The Goetia
There are a lot of ancient grimoires with collections of powerful spirits or demons you can summon to Make Stuff Happen professionally. The Goetia is just the most common one today; mostly because (you guessed it) Aleister Crowley was involved in publishing a modern edition of it (with some help from Macgregor Mathers, the founder of the 19th century magical order known as The Golden Dawn). The Goetia is a book that lists 72 spirits, their 'sigils' or seals that you need to summon them, and the ritual to do so. Each of the entities are said to have a variety of different powers that they can grant a magician who has the focus to bind these demons to their Will. Some of these powers are clearly metaphorical. Others are very direct and literal. The spirits are sometimes described as 'demons' or 'evil spirits', but are more accurately thought of as "rebellious spirits", that are difficult to control for anyone who doesn't have the right training, discipline, level of initiation and/or force of Will. If you try to 'mess' with the Goetia in a sloppy or unprepared way, it can end up messing with you instead.
13. Enochian Vision Magic
Enochian magic is the system created by the 16th century English wizard John Dee. It too involves the communication with spirits, only this time with 'angels' rather than 'demons'. But be warned: these are not the cuddly new-age gentle cherubs that bring 'love and light' or other such bullshit. If anything, the things occultists call "angels" are way more dangerous than the ones they call 'demons'. These guys are superpowerful alien entities; the type of dudes with flaming swords and dire wrath. There's also an entire alien language, which can be used to receive visions of other planes, and visiting these other planes will fundamentally change you as they reveal the nature of occult reality, and your place in it. It's very advanced stuff, but not because it's very hard to do; on the contrary, the thing about Enochian magic is that it will almost always work; but unless you're very careful, not in the way you think it will work. It's a case of 'be careful what you wish for'.
There's lots of books on Enochian magic; starting with Dee's own diaries. And of course Crowley wrote about it too. But probably the most straightforward and easiest guide is, once again, Lon Milo Duquette.
14. The Book of the Sacred Magic of Abramelin The Mage
Another ancient medieval grimoire, the Book of Abramelin has a very special place in western occult practice. It is dedicated to a single massive ritual, taking from 6-18 months of daily work to complete. If you succeed at it, you will obtain the "knowledge and conversation of the holy guardian angel", which is medieval-speak for a direct line to your True Will or Higher Self. It doesn't make you perfect or something, but all the barriers to 'knowing yourself' just vanish. After that, you can understand what you're really meant to do, and accomplish stuff you never would have imagined before. This is considered one of the main goals of every spiritual occultist, but obviously shouldn't even be tried without a lot of prior training and experience. And here's the dangerous part: if you start and then quit before finishing it, you will at the very least be MASSIVELY messed up by this for years.
There are two modern English translations of this book: a 19th century translation by Macgregor Mathers, and a much more recent one by Georg Dehn. The Mathers version is based on an imperfect earlier French translation; the new one is based on the earliest German manuscript and is much better.
15. The Secrets of Western Sex Magic
Sex magic is not really as important as attaining to the True Will, but it sure is... well, sexier. And therefore more popular. Every occultist seems to want to learn it. And there's good reason for that: sex magic has power. It's powerful because sex is powerful; it's one of the most basic human forces. Hell, one of the most basic forces of life itself.
It's surprisingly hard to learn decent sex-magic. You can join a himalayan tantric order, if you can find a real one, and they let you in, and you spend years of basic training to get to the good stuff. Or you can join some western secret society like the OTO and if you're one of the lucky 1% or so who get to the very highest degrees you'll be shown some tricks. Or you can read up on 'chaos magic' techniques, which are mostly about masturbating to home-made sigils. But "The Secrets of Western Sex Magic" is probably the best book you can get without getting to all that trouble.