How do I form the pluperfect subjunctive?

In Spanish, the pluperfect subjunctive (pluscuamperfecto de subjuntivo) refers to an action in the very distant past, much like the pluperfect indicative (había/habías...-ado/ido). However, the subjunctive can be used in conjunction with 'si', just like the imperfect subjunctive. The difference between the two subjunctives is that the pluperfect infers regret over an action that has happened, whereas the imperfect refers to a hypothetical situation. Here is how we conjugate the pluperfect subjunctive:

Take the auxiliary verb haber and conjugate it into the imperfect subjunctive as follows:

(yo) hubiera 

(tú) hubieras

(él/ella/usted) hubiera

(nosotros) hubiéramos

(vosotros) hubiérais

(ellos/ellas/ustedes) hubieran

Then simply conjugate the verb you wish to use into its past participle (e.g. hablar --> hablado).

REMEMBER! 

Some verbs are irregular in the past participle.

The pluperfect subjunctive is often followed by the conditional perfect (condicional compuesto), and this is highly regarded by examiners at A Level.