I had a teacher who used to give us very short stories with all the verbs in the past simple. She asked us to read and whenever we came across an action in the story she would stop us and ask us 'WHEN'. I don't know if that is the best way possible but it worked. We learnt that very often we don't need the past perfect because the context makes time reference clear enough, but there are a lot of time that we have to use it to avoid ambiguity or just to make the sequence easier to understand. I hope this will help you; and for your students' sake, use funny stories; my teacher's used to be very dull.