El uso de used to

Se usa used to + verbo para hablar de habitos ya pasados y para hablar de estados pasados.

Ejemplos:

Hábito: I used to play the guitar. Significa que antes tocabas la guitarra pero ya no.

Estado: I used to live in London. Significa que antes vivias en Londres pero ya no.

Se forma: se usa la misma forma con todas las personas

Afirmativos:

I
you
he/she/it + used to + verbo
we
they

ejemplo: I used to play football, he used to play football, we used to play football etc...

Negativos:

I
you
he/she/it + didn't use to + verbo
we
they

ejemplo: I didn't use to play football, he didn't use to play football, we didn't use to play football etc...

Preguntas:

Did + use to + verbo
ejemplo: Did you use to smoke? (¿Solias fumar?)
What did you use to do....? (Que solias hacer...?)

Ejemplo: Did you use to play football? Did he use to play football?......

Respuestas cortas:

Did you use to play football? (¿Solias jugar al futbol?)
Yes I did
No I didn't

Fuente: http://curso-gratis-ingles.euroresidentes.com/2006/03/el-uso-de-used-to-en-ingls.html