past tenses

CONTRASTING PAST TENSES

Finished / unfinished actions
We use the past simple to talk about a finished action: He read the newspaper, but he didn't find anything interesting. (We know that he finished reading the newspaper.)	We use the past continuous to describe an unfinished activity: At half-past nine he was reading the newspaper. (We don't know if he finished reading the newspaper, because we don't know what he did after half-past nine.)
The past continuous is often used in combination with the past simple ; the past continuous describes an activity which was in process when it was interrupted by the action in the past simple : He was watching the football match when his wife came in . (The action of the wife coming in is finished, but we don't know if the man finished watching the match because his wife's arrival interrupted him.)
We use the past simple to say what someone did in the past, when it is no longer possible for them to continue doing that activity: She wrote six poetry books. (Now she writes different things, or she has stopped writing, or she is dead.)	We use the present perfect to say what someone has done so far (=up to the present), when they can continue doing that sort of thing: He has written three books. (He can continue writing books.)
Stories
We use the past continuous to make a description in a story: The old man was listening to the radio. (We are describing a scene, as if it was a photograph).	We use the past simple to narrate the events in a story: Suddenly, he heard a loud crash and the door opened . (We are telling what happened in the story, as if it was a film).
Pieces of news
We use the present perfect to give a piece of news: I have had a car accident. (The important information is what has happened, not when.) We can use just to express that the event has happened very recently: I have just phoned for a breakdown truck.	We use the past simple to ask for or give details about a piece of news that we have already mentioned: How did it happen ? I didn't see a patch of ice and the car skidded out of control and hit a tree.
Past experiences
We use the present perfect to ask or talk about past experiences, when the time is not important: Have you ever travelled to Italy? Yes, I have visited Rome three times. (We are not interested in when it happened, only in whether or not it has happened, or how many times it has happened).	We use the past simple to ask about a specific experience in the past: When did you last visit Rome? I went on a school trip by coach. (We want to know when it happened, or we know it happened in the past.)
We use the past simple for finished actions in the past: Yesterday I had to take a taxi to get to work.	We use the past perfect for finished actions which are previous to the ones that we have mentioned before: I had got up too late to catch my usual bus because I had forgotten to set my alarm clock.
Events during a specific period of time
We use the present perfect to say how long an action that continues up to the present has happened: She has worked in England for three months. (She still works in England.)	We use the past simple to say how long an action which is no longer happening lasted in the past: She worked in London for two weeks. (She doesn't work in London any longer.)
Situations or states during a specific period of time
We use the present perfect to say how long a situation that continues up to the present has been the case: He has known his wife for thirty years. (He met her thirty years ago, and she is still alive.) They have been married since 1990. (They are still married.)	We use the past simple to say how long a situation which is no longer true lasted in the past: They were friends for twenty years. (They are no longer friends, or one of them is dead.) They met regularly from 1990 to 2010. (They no longer meet regularly.)
Past activities ¹
We use the past continuous to describe the activities during a specific time: We were dancing all evening. What were you talking about with that girl? (I am describing or asking about the activities of that evening or a moment ago).	We use the past simple to ask for or give detailed information about an activity: What did you talk about at the meeting? We only talked about the school trip. Did they say anything interesting? (I am asking for complete information or informing you about what the activity consisted in).

¹ The difference is not very clear in either English or Spanish:

¿De qué estábais hablando? = ¿De qué hablásteis?
Estuvimos viendo una película. = Vimos una película.

Basically, when we use the past continuous we are describing an activity during a specific period of time, and when we use the past simple we are giving more comprehensive or complete information.