In Light on Yoga, BKS Iyengar says that we should practice these 4 seated poses in preparation for Pascimottanasana (Seated Forward Bend)

Janu Sirsasana - Seated Tree

Ardha Baddha Padma Pascimottanasana - Half Lotus Forward Bend

Trianga Mukhaikapada Pascimottanasana Half Hero Forward Bend

Marichyasana I Seated Sage Pose

He says that we should practice them everyday until we can fold forward in Pascimottanasana easily and clasp our hands around our feet.  Then, once we can do that, we only need to practice these poses twice a week.