A. REGULAR AND IRREGULAR IMPERFECT FORMS
1. Regular:
ayudar 
ayudaba, ayudabas, ayudaba, ayudábamos, ayudabais, ayudaban (used to help)
atender atendía, atendías, atendía, atendíamos, atendíais, atendían (used to pay attention to)
asistir asistía, asistías, asistía, asistíamos, asistíais, asistían (used to attend)
2. Only three verbs have irregular forms in the imperfect:
| ir: | iba ibas iba íbamos ibais iban |
ser: | era eras era éramos erais eran |
ver: | veía veías veía veíamos veíais veían |
B. USES OF THE IMPERFECT / USOS DEL IMPERFECTO
1. To describe in the past: the background or setting, situations, conditions, and actions that were in progress (was/were …ing):
| Eran las seis. Tenía doce años. Estaba enfermo y leía en cama. Afuera llovía. De pronto… | It was six. I was twelve. I was sick and was reading in bed. It was raining outside. Suddenly… |
2. To describe habitual, customary actions, or things that used to happen in the past without specific reference to a beginning or end (imperfective, incomplete) (used to, would):
| Iban al cine todos los viernes. Iba mucho al parque cuando era joven. Estaba informada porque leía mucho. |
They used to go to the movies every Friday. I would to go the park a lot when I was young. She was (and stayed) informed because she (habitually) read a lot. |
This means that time expressions conveying repetition are often clues for selecting the imperfect: con frecuencia, cada semana, siempre, a veces, etc.
Tip: Whenever you could say used to or was/were…ing in English, you need the imperfect in Spanish.
Practice
Fill in the blanks with the correct form of the imperfect.
It was Tuesday, November 12. It was six in the morning. Few people were walking by the street. Some pedestrians were heading work, still half-asleep. It was cold, but it wasn’t raining or snowing. There were some cars, but the traffic wasn’t heavy. We were in winter already. From my window, I was seeing people walk by. Usually, when I took my morning coffee, I was serene, content, alert. Nothing bothered me. There was magic in the fresh air. Both people and nature seemed a bit lazy in the morning. The sky was gray, but I wasn’t feeling melancholic.
_______ el martes doce de noviembre. _______ las seis de la mañana. Poca gente _______ por las calles. Algunos peatones _______ hacia el trabajo, todavía medio dormidos. _______ frío, pero no _______ ni _______ . _______ algunos autos, pero el tráfico no _______ pesado. Ya _______ en invierno. Desde mi ventana _______ pasar a la gente. Generalmente, cuando _______ el café matutino, _______ sereno/a, contento/a, alerta. Nada me _______ . _______ magia en el aire fresco. Tanto la gente como la naturaleza _______ un poco perezosas por las mañanas. El cielo _______ gris, pero no _______ melancolía.
(source)