Past perfect simple
1. We use this tense to make it clear that something happened before another event in the past. We usually need to use it if the events are not described in chronological order.
– Chris was amazed. Nothing he had ever seen had prepared him for this.
Once the time reference is clear, it is not always necessary to use the past perfect for all verbs.
– By the time I was 21, I had lived in four different countries. I lived in England until I was five. Then my parents emigrated to New Zealand, where I went to school, and then I went to university in Australia. Finally I ended up doing my PhD in California.
2. We may also use the past perfect to make the order of events clear when conjunctions such as whenand because are used.
– She switched off the TV when he walked in. (=he walked in first)
– She had switched off the TV when he walked in. (=she switched it off first)
With conjunctions such as before, after and as soon as, the past perfect is optional as the order of events is shown by the conjunction.
– The bell rang before they (had) finished.
Past perfect continuous
This tense describes a continuing or repeated activity or event leading up to a particular time or event in the past. The event or activity may stop just before or at this point, or it may continue.
– By 1982, Marris had been teaching disabled children for nine years.
– She’d just been swimming, and her hair was still wet.
Both of these can describe past habits (often long ago rather than the recent past).
1. used to can describe habitual actions, repeated actions and states.
– When I was six or seven, I used to enjoy spending holidays with my grandparents.
2. would is used for habitual or repeated actions (but not for states) when a specific time period is being referred to.
– Sunday mornings at the cottage were always the same. My grandfather would get up early and milk the cows while my grandmother got* breakfast ready.
* As with the past perfect, once the time referred to has been established, it is not necessary to continue using would or used to with every verb.