To become a Google Certified Trainer, check out the “Become an Apps Certified Trainer.” There is a great Training Center and then you will take six exams. After passing all six exams, you become a Qualified Individual. The last step to become a Certified Trainer is to fill out an application and produce a two minute video “which demonstrates your ability to create and present instructional material.” (Program Details) Even if you are not interested in taking the tests, I would recommend using the training center to learn a great deal of information about Google Apps.
Here is the video that I produced as part of the application process. It is on Google Calendar Labs.