There really doesn't seem to be any definitive book on Crowley's deck other than his own The Book of Thoth (Egyptian Tarot), U.S. Games Systems Inc. ISBN 0-913866-12-1. But Crowley writes a rather difficult read and can tend to digress and then smoothly move back into his subject while appearing to flatly deny ever having digressed in the first place.
That said, a real understanding of the cards requires a knowledge of Astrology and Western Qabalah to such a degree that the inherent wisdom of those systems alone will change your life.
My way of having learned the cards and my method is probably pretty stupid. I've learned over the years through the use of many many many different decks (Thoth being my favorite) and not only am I familiar with the systems I mention, but I remember every card with near picture perfect clarity (and since every LWB I've read has shown only minor variations in "keyword" meanings, I have them down pretty nicely too). So, when I draw a card, say the 6 of Disks for example, not only am I aware of what it means to place Tiphareth in Assiah and the Moon in Taurus (altogether a wonderful sense of togetherness), and not only do I see the harmony in this picture that Harris painted, but I remember the image of the RWS deck of the little boy giving a flower to the little girl, and the image on the New Vision deck where the proud parents are involved behind the card, and the Mythic Tarot's image of a man seeking payment or a loan from his King (and so on for other decks), and I also know through my learning that his card denotes success in material matters - not the grandest of riches but just enough to let you know that you can drop quarters in that charity box at Burger King, just enough to let you know that you can offer that loan to your brother he's been wanting. Or given the reverse of this card for some reason (I don't usually use reversals, but prefer pairings and dignities), the need for such a thing.
It doesn't matter what deck is used. No one has ever proven to me that for divination purposes Crowley invented a new deck with new meanings. What he did do was send us new energy and a new paradigm within which to examine these meanings.
It's a great deck.