Used To vs Would
Both 'used to' and 'would' can be used to describe past habits, but there are important differences.
Used To
Can be used for both past habits and past states (things that were true but are no longer true).
I used to smoke. (Past habit) I used to live in Paris. (Past state)
Would
Can ONLY be used for past habits or repeated actions, never for past states.
Every summer, we would go to the beach. (Correct - action) I would live in Paris. (Incorrect - state)
Negative and Question Forms (Used to)
Negative: Subject + didn't use to + base verb. (I didn't use to like vegetables.)
Question: Did + subject + use to + base verb? (Did you use to play piano?)