Used To vs. Would (Part 2)

If you want to talk about repeated states or habits in the past, you must use used to, you cannot use would :
My dog used to bark at cats.
I used to smoke.
I used to be an administrative assistant.
I used to live in England.

You should use 'use to' without a d in sentences when it follows 'did' or 'didn't' (don't worry too much about this because lots of people get it wrong).

The question form is ‘Did you use to…?'. When asking a closed question you put did/didn't in front of the subject followed by use to, you cannot use would.
Did you use to go out with my sister?
Did they use to own the company?
Didn't we use to go to the same school?

Also when asking questions about states in the past you cannot use would.
What sort of things did you use to like when you were young?

In the negative you cannot use would without a change in meaning:

I didn't use to play with my dolls.

If I said I wouldn't play with my dolls. It would mean I refused to play with my dolls.

We didn't use to go out much in the winter months.

If I said we wouldn't go out much. It would mean we refused to go out much.

!Note - The general rule is when there is did or didn't in the sentence, we say use to (without d) when there is no did or didn't in the sentence, we say used to (with d).

taken from:

http://www.learnenglish.de/grammar/usedtotext.html