The key to good teaching is to talk about what you already know. You may not be perfect at GTD, you may not even have read the book yourself, but you've read what you have read and you've implemented what you've implemented -- and you've seen some results. It might actually work to your advantage to teach only what you know and to just simply admit that you are still in the learning process. If you present GTD as something you have to know par excellence in order to do it then others are going to think they have to know it all perfectly or they won't be able to implement it at all.

Just go for it. Don't represent yourself as a GTD expert -- just a GTDer in training. You are probably enthusiastic about it because there are some things that are working for you. If others connect with your enthusiasm and would like to get things together the way you have, that's all you really need.

Eventually we all have to learn it on our own anyway. I say "go for it" and just be honest about where you are in the process. That will be all the encouragement the others need to get started and then you can point them to the resources they would need to learn more.

Todd V