Form and rules
How it works
Past simple normally carries the main sequence of completed narrative events; past continuous creates background or interrupted activity.
Past perfect locates a completed event before the main past reference point; past perfect continuous emphasizes earlier duration or repeated activity.
Used to can describe former states and repeated actions; habitual would normally describes repeated actions, not states.
Once an earlier time frame is established, writers often return to past simple instead of keeping every subsequent verb in past perfect.
Narrative tense choice is partly about viewpoint: the same event may be foregrounded as a whole or backgrounded as an activity in progress.