I'm skeptical about such endeavors. I mean, even I will quote LRichard by saying that it is like driving a sports car to the grocery, what is proposed as "keywords" or whatever is actually counterproductive for study of the Thoth, as it gets you used to bad habits that are very difficult to give up later on. People keep saying that this or that might lead people to study more deeply, but why would anyone send anyone to a book where they would first learn mistakes and then spend time unlearning them? This is what Mirror of the Soul, along with its even worse companion, Mirror of your Relationships, do. Even the keywords book is an abomination. Both of them completely miss the point.
The Thoth Tarot is difficult. When you try to simplify it you end up with Angeles Arrien or, yes, Zeigler. But why the uncontrollable urge to make everything easy for beginners, byte size, approachable, friendly, etc. Not only isn't it any of those things, it also shouldn't be, because it deals with issues that are too serious to be. Why not make everything beginner level, like astrophysics?
I this might sound like the grumbling of a purist, but there really is more to it than that. Coming to terms with the difficulty of the deck is part of the study itself. If you can't handle it, or don't get it the first time around them you try again and again. And again. And again still until you do. But going the "easy, practical" route... well, honestly, this is why I usually don't help the odd request for interpretations here on the Thoth forum. This is because people don't do the work, they don't go the extra mile.
If you find the Thoth easy, or try to make it so, you're doing something wrong. If you find it mysterious and enthralling and consuming and a constant challenge, then mazel tov, you're on the right track.