How do you know when to use the imperfect or preterite past tenses?

Preterite- would be used for SINGULAR actions in the past; completed actions Imperfect- repeated actions in the past( saying I used to do something...) or descriptions We generally say that imperfect is a "background tense" When used in the same sentence: IMPERFECT- something that WAS GOING ON; and PRETERITE- something specific that happenedExamplesCuando trabajaba en Starbucks... (When I worked in Starbucks- IMPERFECT USED HERE as "I used to work") conoci a mi novio. (I met my boyfriend- PERFECT USED HERE, as only met my boyfriend once)