Pretérito vrs imperfecto

El Pretérito
 Use the preterit tense to state specific actions completed in the past.
Pedro salió del colegio y caminó hasta el café.
Pedro left school and walked to the café.
 Use the preterit tense to say an action that interrupts another action in progress in the past.
Yo miraba la televisión cuando sonó el teléfono.
I was watching television when the phone rang.
 Use the preterit tense to say what day it was or what the date was in the past.
Ayer fue lunes.
Yesterday was Monday.
 Use the preterit to state that you did not do something.
No fui al banco.
I didn’t go to the bank.
 Use the preterit tense to mark the beginning or the end of an action.
I started to play the guitar when I was 8.
Empecé a tocar la guitarra cuando tenía 8 años.
 Use the preterit to state an action that took place during a specific period of time.
Toqué el piano por 6 años.
I played the piano for 6 years.
 These words or phrases are commonly followed with actions in the preterit tense:
 Un día, ese día
 Una vez, raras veces
 El lunes/martes/miércoles, ect.
 Nunca
El Imperfecto
 Use the imperfect tense to say habitual actions in the past, without focusing on their beginning or end.
Yo siempre salía del colegio y caminaba al café.
I always left school and walked to the café.
 Use the imperfect tense to tell what time it was in the past.
Eran las dos y cuarto de la mañana.
It was 2:15 A.M.
 Use the imperfect tense to ‘set the scene’, or describe actions that were in progress in the past.
Felipe y José bebían café y escuchaban música.
Felipe and José were drinking coffee and listening to music.
 Use the imperfect tense of estar and a gerund to express the past progressive.
Pilar estaba corriendo cuando se cayó.
Pilar was running when she fell.
 Use the imperfect tense to describe the weather in the past.
Estaba nublado y hacía frío.
It was cloudy and it was cold.
*ojo* Weather that is considered a completed ‘event’ is told in the preterit:
Hubo una tormenta.
There was a storm.
 Use the imperfect tense to describe physical or personality characteristics of people in the past.
Mi mejor amiga era alta, tenía el pelo oscuro, y era muy simpática.
My best friend was tall, had dark hair, and was very nice.
 Use the imperfect tense to describe physical or emotional states of being in the past.
El bebé estaba impaciente porque tenía mucha hambre.
The baby was impatient because it was very hungry.
 Use the imperfect tense (with ir+a+infinitive) to state a future action planned in the past (something that you ‘were going to do’).
íbamos a salir, pero empezó a llover.
We were going to leave, but it started to rain.
 These words and phrases are commonly followed with actions in the imperfect tense:
 Todos los días
 Cada año
 Mientras (que)
 Siempre
 Muchas veces

Preterit Vs. Imperfect:
Remember, Spanish has two past tenses: preterit and imperfect. Most verbs can be put into either tense, depending upon the meaning. The preterit tells us specifically when an action took place. The imperfect tells us in general when an action took place.
Some words and phrases indicate specific time frames, and therefore signal the use or the preterit:
Preterit
Ayer (yesterday)
Anteayer (the day before yesterday)
Anoche (last night)
Desde el primer momento (from the first moment)
Durante dos siglos (for two centuries)
El otro día (the other day)
En ese momento (in that moment)
Entonces (then)
Esta mañana (this morning)
Esta tarde (this afternoon)
La semana pasada (last week)
El mes pasado (last month)
El año pasado (last year)
Hace dos días, años (two days-years ago)
Ayer por la mañana (yesterday morning)
Ayer por la tarde (yesterday afternoon)
Other words and phrases indicate repetitive, vague or non-specific time frames, and therefore signal the use of the imperfect.
Imperfect
A menudo (often)
A veces (sometimes)
Cada día (every day)
Cada Mes (every month)
Cada año (each year)
Con frequencia (with frequency)
De vez en cuando (from time to time)
En aquella época (at that time)
En aquél entonces (back then)
Frecuentemente (frequently)
Generalmente (usually,generally)
Muchas veces (many times)
Mucho (a lot)
Nunca (never)
Por un rato (for a while)
Siempre (always)
Tantas veces (so many times)
Todas las semanas (every week)
Todos los días (every day)
Todo el tiempo (all the time)
Varias veces (several times, various times)