It may not work for you, but I'll tell you what worked for me. I looked at passing the written, passing the oral and being a good flight instructor as three different things. I also came in with some non aviation instruction experience, so that helped. The short version of the story of passing my FOI written is I borrowed the Gleim book from a friend and read the question bank over and over one evening. I'd read the question and ONLY the correct answer. If I remember right, there are only about 200 questions so it didn't take that long. The next morning I drove to the test site, and reread all of the questions and answers again in my car in the parking lot before walking in. When I actually took the test, it was a breeze. The correct answers jumped out at me, nothing else seemed right. I answered all the questions and double checked them in fifteen minutes flat. When I walked out of the testing room, the proctor told me that I can't leave the room before my test was over. I told him I was done and he gave me my results with 100% on top.
This method will certainly offend some people, and they might even so far as to call it cheating. I call it doing what works. I can also say that I knew the information.
For the oral, I was able to fit all of the memorization stuff on one piece of paper. All the types of questions, the stages of learning and so on. If you can memorize those simple lists and hold a good conversation, you should be fine on the oral. I passed the Light Sport Instructor with a DPE and the CFI with the FAA both on the first try.
I'd say the most important thing to being a good instructor is having good CFI mentors wherever you end up working. Short of that, I was really helped by a few education books, including Punished by Rewards. The books that have helped me the most haven't been about teaching, but just relating to people. My favorite there would be Shambhala: The Sacred Path of the Warrior.
Hope this helps!