Question: How to Serve Guru?
In what ways can a devotee serve his spiritual master in this age? What kind of spiritual duties does Spiritual master give?
Answer: Dedicate Your Life to His Mission
Since the spiritual master is fully absorbed in trying to save the fallen, conditioned souls of this world from the repetition of birth and death, the best service that you can render to him is to fully dedicated your entire life to assisting him in his mission.
When you fully surrender yourself at the lotus feet of the bona fide spiritual master he will engage you in whatever way you can best assist him according to your talents and propensities.