How can a disciple best train himself/herself to serve the guru?
What do you mean by service? Generally when people think of service they think of manual work in which one is involved not just in thought or emotion, but physically. That is not service because your body is going to perform its karmas, your mind is going to perform its karmas. Whether or not you have an attitude of service, you are still going to perform these karmas in that situation. No one is free of karma.
As a disciple one has to learn to manage the plays of the ego by maintaining one's simplicity and innocence, by not being devious, crooked and an opportunist, by not hankering to fill someone else's shoes, but by being what you are. This is a very intense and deep sadhana. It is one of the greatest challenges in front of a disciple. You think, I have surrendered to this person or this image or this God. Thoughts are common. Some are fleeting; they come and go. Some are semi-resident; you think about them for a few months and then they disappear, like a visitor who spends a few days in your home and then goes. Some thoughts are permanent and they become part of your swabhav, your nature, your personality.
Many thoughts are associated with the idea of competition, many are associated with the idea of getting recognition. It is natural for everyone. Many thoughts are associated with the idea of being able to rule or govern people. One likes to be the master, whether of one servant or ten it doesn't matter. Then there is the desire for holding power, personal greatness and grandeur: I can speak better than that person, That person works for eight hours; I can work for twelve hours without stopping. This is how the ego, ahamkara, slowly raises its head.
Certain ideas are implemented in the mind by the ego principle. When they become permanent and a part of our nature, they become a barrier in the proper relationship between the devotee and the Lord, the disciple and the guru, man and God. This is the barrier in the relationship. The greatest challenge in front of the disciple is to manage the ego by maintaining one's innocence, simplicity and truthfulness. Truthfulness reflects in the human character as a quality, not arrogance. If there is a reflection of arrogance, jealousy, anger or hatred in your features then you have definitely failed.
These are the keys to becoming a useful tool in the mission of service of the spirit of the guru.
—Ganga Darshan, 24 August 1998