That's a tough question to answer because, to genuinely answer it, a person needs to have read all the books :)

I haven't read all the books though I've scanned a few - so I can't give you a definitive answer - however I can point out to you something within your question that you might wish to think about.

If you are asking already about which other of his books you are going to read next, isn't there a hidden assumption in that question that you are not going to find everything you need in the Master Key System?

Isn't that an assumption that is implying that there is still something out there in physical reality (in some other book by Haanel or others) that holds a further yet-to-be-found key? I've noticed that our assumptions (hidden or not) tend to be reflected in our physical realities.

I spent many, many years looking for more and more answers out there and kept finding more and more answers out there to match that assumption...but my life still didn't actually improve that much...I just found more and more answers out there, that's all :)

Having a lot of knowledge from out there can be useful for coming up with - or, perhaps boring people with :) - answers on Inward Quest but as far as genuinely improving your life situation is concerned, it might not be as helpful as it first seems.

What finally made the difference for me was to change my assumptive attitude from one of being a searcher for answers to one of being a knower that I already had all the answers within myself and now all I had to do was to find ways to allow those answers to come to me.

If you hold an assumption (technically, a presupposition) that you already have the answers, your life goes in a different direction to one who is holding an assumption that they need to keep searching.

Probably not a helpful answer to your actual question, but just something to ponder :)

I think Stingray's answer above is one of the best (if not the best) answers I've read on this site. Everything you need to know is already within you and I think every real teacher and every real teaching points the way toward that. You'll only need the books until you realize that you don't need them

The search and the questions themselves are what keep us stuck. They're needed only until we realize fully that they are not needed.Our greatest teachings about ourselves already exist in our day to day reality. Every relationship and situation we create hold the greatest potential for our own individual evolution if we're willing to take a good honest look at ourselves and the part we played in the creation. Fear can only be realized for the illusion that it is when we look at it face to face.

Personally the past couple of years have been the toughest part of my own awakening but I am the one who called forth my own spirit because I want the Truth and nothing less. I know beyond a shadow of a doubt that I've called forth those parts of myself that I stuffed in the basement so they could come forth into the light of awareness for healing. I've noticed that in a sense we almost recreate situations that our younger selves did not have the awareness to deal with but our more mature self can now see how and why we did what we did...evolution and freedom rolled into one. Self awareness is the only key to what everyone's looking for and the only route there is outside one's own individual comfort zone.

As for the order you should read the books, the right one will show up exactly when you need it...don't overthink it.

And Kakaboo the simple answer to your question...stop searching and the knowing will come forth all by itself. It's not something you can try to do but rather something you allow.

Stingray shared some good wisdom in making a decision to apply what one's learned. However I do cheer anybody who continues seeking knowledge.

I'm working on The Master Key System because the cognitive exercises will add to my Chi Kung exercises. I'm currently on Part 9. I will add my answer to the question of what sequence of reading is suggested.

The Master Key System is a twice daily practice. Each Lesson can be read in less than 30-minutes and the practice takes at least a week or more for each lesson. In the meantime why not read something else? My suggestion is a Charles F. Haanel book entitled You because of the author's discussion upon energy and vibrations. These same topics are covered in The Master Key System. I will begin reading the book entitle You very soon even as I advance in cognitive skills from practicing skills prescribed in The Master Key System. I believe any additional knowledge along the way enriches one's understanding.

If perchance there is an low confidence upon what one reads, Skills learned from The Master Key System should increase one's self-confidence. Eventually an overly seeking minding without applying knowledge found will lead to a realization that many books are repeating what was read by an earlier book. That said, some author writing styles will click with a reader while others won't stick or add growth. From the many books that resemble each other, a writing style will connect and bring growth that leads to confidence in what one is doing.

Another author offering meditation techniques and energy philosophy is Mantak Chia with his many Chi Kung books (see Amazon.com). Mantak Chia writes about Universal Energy and Cosmic vibrations with meditation techniques to facilitate making such cosmic connections with light and color energy.

Summary, The Master Key System is a twice daily practice, meanwhile other books may be read during one's day. Perhaps finding a book to compliment The Master Key System. Charles F. Haanel's book entitled You should be a timely compliment for it's topic on energy and vibrations. Have my best wishes.