First a warning: In the event of a breakdown think road safety; have you got a hi-visibility jacket for yourself and passengers, if so wear it. Can you place a warning triangle, or a person safely, back down the road, but make sure you collect the triangle and person afterwards.
A methodical approach starting with the connections and then work back from the plugs, checking that the spark is reaching that point in the system.
This article, written by Andrew Jarmin, originally appeared in CA7C Seven Focus in Jun 2006 pp16-18, following one of the Club 'Teach-ins'.