There are several ways to express regrets about the past
or "I should have..."

The most formal method, uses the following formula:

debiera
debieras
debiera + haber + past participle
debiéramos
debierais
debieran

Debiera haber lavado el coche.
I should have washed the car.

A second method uses the following formula:

debí
debiste
debió
debimos + haber + past participle
debisteis
debieron

Debí haber hecho la tarea.
I should have done the homework.

The least formal method uses the following formula:

hubiera
hubieras
hubiera + past participle
hubiéramos
hubierais
hubieran

Hubiera prestado atención a mi papá.
I should have paid attention to my father.

There are many factors that will determine which of these three constructions you should use. There are not only regional differences among the three, but there are differences
in tone as well.

[ view complete lesson ]