50 You must see to it that earnest and unceasing prayers are offered by your priests and faithful in furthering this holy purpose. Instruction of the faithful concerning the life of the Church will supply, as it were, food for this prayerful devotion, as We have already indicated. Devout souls should be exhorted to greater efforts in prayer at definite times during the liturgical year that seem to be more suitable for fostering and promoting interest in missionary work.
Source: Fidei Donum (Vatican.va)