You have to complete the AOPA ground instructor course, (an entrance examination will be required before you commence the course), then take an exam at the end, on which you have to demonstrate required knowledge in all ground subjects, plus give the examiner a long briefing of his/her choice. Afterwards, you will be subject to a 'questions and answers' session.
During the course, you will be expected to give various lectures/briefings on any of the seven PPL subjects.
It's worth mentioning that BEFORE undertaking any of this, in order to become a ground instructor / examiner, you will have to be nominated by an FTO or RTF, then become affiliated to them before applying to the CAA for certification.
AOPA should have a list of establishments carrying out the course; alternatively, some advertise in the back of the popular flying magazines
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