Send me a PM today, and we'll arrange for you to purchase my King FOI/CFI written course. The FAA examiner (who has since moved to OK city to train designated examiners) said I was the best prepared initial CFI candidate he had as an inspector. Much of the credit goes to the thorough treatment the Kings gave the material. I was going to put in on Ebay, but I could easily sell it to you. Make an offer.
Start with your FOI (Fundamentals of Instruction) which in FAA parlance is the Aviation Instructors Handbook.
Make sure you get the proper PTS (there are 4 for the CFI series, Single engine, Multi engine, Rotor and Instrument). If you are just studying for a CFI-A, get the single engine.
Finally, I like William Kershner and have his entire series of books. He has an Instructors Handbook. You have to be a little math oriented, a little twisted and you need to study from some other source, but he captures subjects that nobody else will touch.
Get with your CFI (if he is eligible for CFI signoffs - read the rulebook) and just learn to fly right seat. After you are comfortable and can land from over there, start doing all the PTS manuevers. You will be "ham-handed" for about two flights and then you won't care that your left hand is on the throttle, the right hand moves the yoke and the instrument panel is about two miles to your left.
Be sure you obtain the PTS's for the instructor certificate(s) you're seeking. Each PTS will provide references to FAA materials on which the practical is based.
I like Kershner's Flight Instructor's Handbook and I always used ASA books to prepare for the writtens. The bottom line, though, is the FAA's materials are the final, official word on what you must know to teach and how to teach it.
You do have to know the FOI for your initial practical; I've even heard of some examiners who quiz people on it for add-on instructor ratings. I do suggest that you take the time and effort to learn the material in the FOI beyond rote memorization. I found that after I studied it and understood it I found that the really worked and gave me insights about how people learn and how to deal with them.
You find that takeoffs and normal flying are about the same in right seat as from the left seat, but landings are strange at first. What really is surprising is how much coordination transfers between hands.
I used a lot of the FAA publications (flying handbook, aeronautical knowledge, and the instructors handbook) to prepare for the exam. They actually work pretty well. Just finished up with the first part of my CFI initial checkride today. The gory totals: 5 hours of oral so far, and am going back for more tomorrow (had to discontinue due to alternator failure). My FAA examiner has put a VERY strong emphasis on the FOI's (1.75 hrs). I was caught a little off guard and felt embarassed that I was not fully prepared.
Well, I'm off to get rested up for another 2 hours of oral and a 2-3 hr flight in the AM. Yipee ki-ae!
I said what I said because so many people just rote-memorize the FOI. Really, there's quite a bit of value in it. I actually took the time to learn it, primarily through having CFI trainees as students, and found that it helped my work immensely.