Past tenses

Past Simple (I did)

You use the Simple Past to talk about actions or situations.

I enjoyed dinner very much. 

Past Continuous (I was doing)

You use the Past Continuous to say that someone was in the middle of doing something at a certain time in the past. The action or situation had already started before this time but hadn't finished:

What were you doing at 8:00 this morning?

Often you can use the Past Continuous and the Simple Past together to say that something happened in the middle of something else:

Jeff burned his finger while he was cooking lunch.

Past Perfect (I had done)

The Past Perfect (I had done) is the past of the Present Perfect (I have done):

Present: Our bedroom is dirty. We haven't cleaned it for weeks.

Past: Our bedroom was dirty. We hadn't cleaned it for weeks.

You use the Past Perfect to say that something had already happened before another past event.

When I arrived at the dance, Dick had already gone home.

Past Perfect Continuous (I had been doing)

You can use the Past Perfect Continuous to say that something had been happening for a period of time before something else happened:

The baseball game had to be stopped. They had been playing for an hour when it started to rain.

Used to (used to do)

You use used to to say that something happened regularly in the past but no longer happens:

I used to play basketball a lot, but now I'm too busy. 

We can also use would in these situations:

When I got home from school I would have a snack and do my homework, then I would watch TV.

Would emphasizes the action as being a part of a past routine.

Used to emphasizes the fact that it does not happen anymore.

You can also use used to for past situations (that no longer exist):

I used to live in a small village, but now I live in Prague.

You CAN'T use would in these situations.

BE CAREFUL!

Do not confuse I used to do and I am used to doing.

The structures and meanings are different:

I used to live alone.  (I lived alone but I no longer live alone)

I am used to living alone.  (I live alone and do not find it strange because I have been living alone for some time.)