What is the difference between 'would' and 'used to' or can they both be used interchangeably?
You use used to + infinitive to talk about something that happened regularly in the past but no longer happens.
I used to play tennis a lot but I don't play very often now.
Did you use to collect stamps?
I didn't use to like her.
I used not to like her. (more formal)
Would is similar to used to but we only use used to, not 'would', to talk about states:
I used to be much slimmer when I was younger.
I would be much slimmer when I was younger.