We use Past Simple for completed actions in the past, and we use past continuous for actions that were in progress and not yet finished at a certain point in the past. In addition, a short action in the past simple often interrupts a long action in the past continuous.

Action in progress

  • They were arguing when I saw them yesterday,.
  • They were swimming at 7 in the morning.

Describing a longer action

  • When I met Susan she was having a drink at a terrace with a friend.
  • We didn’t go out because it was raining.
  • He was playing football when he broke his arm.
  • When I went to bed, it was raining.

Describing the beginning of a story

  • It was getting dark, and I was walking fast. Suddenly …
  • Last night I was walking home and listening to my ipod when …
  • The sun was shining and lots of tourists were lying on the beach. Suddenly …

References