When to use Pretérito imperfecto?

Past imperfect tense is used to express unfinished past actions. Remember the following situations:

1. repetitive or regular activities in the past:

Mis amigos y yo veíamos peliculas todos los días. My friends and I used to watch films every day.
Mi madre siempre cocinaba este plato. My mother always used to cook this dish.

2. description of states in the past (state of people, things, etc.):

No fui al cine porque estaba muy cansada. I didn’t go to the cinema because I was very tired.
La casa estaba desordenada. The house was messy.

3. simultaneous actions in the past:

Mientras Miguel leía el periódico María hablaba por teléfono. While Miguel was reading the newspaper, Maria spoke on the phone.
Pablo tocaba la guitarra y cantaba canciones. Pablo played the guitar and sang songs.

4. an ongoing action in the past that serves as background for a completed action:

María hablaba por teléfono cuando alguien llamó a la puerta. Maria was speaking on the phone when someone rang the door.
La guerra empezó cuando éramos pequeños. The war began when we were little.

Remember these indicator words for this tense:

• siempre, todos los días, tres veces a la semana (and other words expressing frequency)

Todos los sábados ibamos a jugar al fútbol. We used to play football every Saturday.
Nos veíamos dos veces al mes. We saw each other twice a month.

• mientras, cuando (words expressing the simultaneity of actions)

Mientras dormía soñaba con vacaciones en el mar. While I was sleeping I dreamed of holidays by the sea.

There are only three verbs that have irregular forms of Imperfecto: