There aren't too many ebooks written specifically on instructing agility classes. However, in preparation for offering classes, you will want to perfect your own skills in general dog training, including breaking down behaviors, setting criteria, formulating and evaluating training plans, evaluating and timing different reinforcers and punishers, using reinforcement schedules in order to identify what dogs in your classes will need. There are plenty of good ebooks available that will help with this. Check out
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You'll obviously want to focus on your own instruction skills as well. You can be the best at agility or any other dog training yourself, but if you lack instruction skills, you won't be a good teacher--trust me, I've wasted good money taking classes from people who are wonderful at what they do, but horrible at teaching others. Look for ebooks that focus on group instruction skills in general. The same strategies and techniques will transfer to agility instruction.
As for agility training specifically, I don't think there are too many e-books available. Agility is something that is easier learned by visual and hands-on learning. I could give you the name of some lovely DVD sets, but I know that you are limited as to what you can get your hands on. If you can get your hands on material from Susan Garrett, it would be worth the investment. Her stuff is mostly for people who participate in agility as a handler, but if you have good dog training skills and instructional skills yourself, you should have no problem transferring what you learn from her material into something to use in your classes. Greg Deritt is another great competitor/instructor who has published some nice material. These will help you perfect your own handling skills so you can better teach others.
You will want to look at each of the sanctioning bodies for agility out there (AKC, NADAC, USDAA, etc.) and see if your region has any of its own. They all have slightly different rules and equipment specifications so you'll need to decide which you will adopt. You should be able to download alot of information from their websites.
Hopefully, the agility instructor you will be working with knows their stuff. If so, perhaps you could apprentice under them for a while to gain some instruction skills and better perfect your own handling skills. I've found
AgilityNerd to be helpful. The site owner is an agility competitor and instructor and there is a large bank of information on the site including videos showing handling skills and lots of different practice exercises that would be easily included in training classes.
You might also consider looking for material on conditioning a canine athlete. Like any sport, there is a risk of injury to the dog. I would recommend reading up on normal dog structure and gait. I believe there is an ebook available on jumping and teaching proper jumping technique. If a dog's gait or jump style is off, there can be huge potential for negative health effects. While agility instructors don't need to be anatomy experts, they should have a basic understanding of the role that structure and conformation has on performance. Instructors should also be able to recognize common structural anomalies and symptoms of certain orthopedic problems that will impact a dog's performance and health so they can keep their clients and their dogs safe.
I will say that Agility taught poorly leaves its mark on both the dogs and the handler students. Make sure you really know what you are doing before you start teaching others. It is hard and discouraging for students to find out as they progress that they have adopted some bad handling habits or inadvertantly mistrained the equipment due to poor instruction. You will be a much more confident instructor if you know you are offering quality instruction. And your clients will be much more willing to come to you if they know that you truely know your stuff.
. I guess what will perfect them now is practice - I already have a ton of books on that subject.