According to the preface, what is considered the most certain and effective form of Guru service for attaining salvation?

According to Chapter 0, the best and most certain service that grants the fruit of salvation is to write the biography of one's Sadguru. This should be done either by the Guru's command or inner inspiration. Furthermore, one must personally study it regularly, performing hundreds of readings (Parayans) and weekly recitations (Saptahs) with a firm resolve, pure heart, excellent faith, selfless love, and unwavering devotion. This service of body and speech does not interfere with one's family life.