Ah, yes, the Book of Thoth. I've never actually done drugs, but I find that if I have a glass of wine and ask someone to read to me from the Book of Thoth, I get a dizzy and surreal feeling that's gotta be similar. Heady stuff. And, if you are in the right mood, very very funny. Crowley was really good at insulting people, but he was so clever about it I bet half the time they didn't even realize they were being insulted. He talks about the lamb of god in one sentence, then about tasty lamb for dinner in the next. Unbelievable!
So most of us find other ways to get insight into the cards.
Honestly, I think the best way in is the pictures. I get amazing readings just looking at the pictures. I found the keywords too demanding, so I cut them off. (The cards now fit together in really neat ways, without their borders.) I guess what I'm saying is that it's Lady Harris whose ideas I enjoy.
But if you really want to know what ole crowl was thinking, that Lon DuQuette book is the most popular. It's chatty and accessible.
"The Crowley Tarot: Handbook to the Cards" by Akron and Hajo Banzhaf is amazing. It is so intensely detailed that I think it actually has MORE information than the Book of Thoth. It discusses the background of each of the symbols that appear in the cards, stuff Crowley probably thought was too obvious to mention. Absolutely amazing level of detail and scholarship. The parts I enjoy the most are the suggested "Analogous Correlations." For each of the majors, the authors mention paintings, stories, musical pieces, gems and neat quotes that they've decided could be associated with each major. For example, they suggest Picasso's "Guernica" for the Tower.