Here's a short answer.
It's a long process. Not only do you have to take the classes,(that's the easier part ).You have to be able to understand thoroughly what you are teaching, be able to present the information and answer questions. Presenting the information in a logical and effective manner is the hard part for most people. Public speaking classes are a must. Staying current on information and skills is an ongoing process.
The other thing that is crucial is the hands on experience. The more experience you have the more credibility you'll have. This means rescue experience and time practicing all of your skills.
Don't expect to pay an organization for certificates and a curriculum and be set to teach, it involves much more than that and the organization will tell you that. There's a lot more to it than following a course outline. Send me a PM if you have questions and hopefully I can help you out.
Mike Duffy
Avalanche1.com