The "conditional progressive" mood is formed using the formula below:

conditional conjugation of estar + present participle = conditional progressive

The conditional conjugation of estar is shown below:

estar (full conjugation)

   
yo
   
estaría
   
(I would be)


   
tú
   
estarías
   
(you would be)


   
él/ella/Ud
   
estaría
   
(he/she/you'd be)


   
nosotros (as)
   
estaríamos
   
(we would be)


   
vosotros (as)
   
estaríais
   
(you guys would be)


   
ellos/ellas/Uds
   
estarían
   
(they/you would be)

The present participle is formed from the infinitive of a verb by removing the (ar), (er), or (ir) ending and adding (ando) for (ar) verbs, and (iendo) for (er) and (ir) verbs:

hablar ---> hablando (speaking)
volver ---> volviendo (returning)

Example sentences:

Juan dijo que estaría esperándonos.
Juan said he would be waiting for us.

Estaría hablando en serio?
Would he be serious?