IMPERFECT-PRETERITE

IMPERFECT:
-An action in the past that has an indefinite period, we don't know when they were finished (ongoing action). They may be over or not. Similar use to 'Verb to be (past) + ing', past continous construction.
I was living in Newyork in the 70´s --- Yo vivía en Nueva York en los 70
He was wearing blue trousers --- Él llevaba pantalones azules
-Actions that occurred repeatedly in the past,but don't know how many times. Similar use to the 'used to …' construction.
I used to eat everyday in that restaurant --- Comía todos los días en ese restaurante
I never used to eat in that restaurant --- Yo nunca comía en ese restaurante.
-When I talk about my age in the past
When I was 18 I used to dance on weekends --- Cuando tenía 18 bailaba los fines de semana
PRETERITE:
-An action in the past that has a definite period, we know when it begins and ends. It is over. Similar to the past simple verb tense.
I lived in New York for 7 years in the 70's --- Yo viví en Nueva York por 7 años en los 70
He wore his blue trousers for 3 days --- Él llevó sus pantalones azules por tres días
-Actions that occurred in the past a certain number of times (one times, several times or never)
I ate 3 times in that restaurant --- Comí tres veces en ese restaurante
I never ate in that restaurant --- Nunca comí en ese restaurante
BOTH COMBINED IN THE SAME SENTECE:
-When we talk about an action that took place at a particular time (preterite) while other action was happening over a wider period of time (imperfect).
She was eating when his father entered the house --- Ella comía cuando su padre entró en la casa
While she was speaking he kissed her --- Mientras ella hablaba él la besó。