When would you use the preterite versus the imperfect?

The preterite tense is used for completed actions in the past, so for example: j'ai joué au foot hier. The action has been done once and is finished.
The imperfect would be used for repeated actions in the past, things that happened over a period of time, were habitual or something you used to do. For example: je jouais au football tous les samedis