According to the provided text, what is considered the most effective form of Guru service through writing, and how should it be performed?

The preface in Chapter 0 identifies the best and most certain form of Guru service through writing as composing the biography of one's own Sadguru. This act can be initiated either by the Guru's command or through a devotee's own inner inspiration. The service extends beyond just writing; it involves a dedicated practice of personally studying the biography, performing hundreds of readings known as Parayans, and conducting weekly recitations, or Saptahs. Chapter 0 emphasizes that for this service to grant the fruit of salvation, it must be performed with a firm resolve, pure heart, excellent faith, selfless love, and unwavering devotion.