How to become a guru? Srila Prabhupada describes the process of how one can become a bona fide guru. It is not by taking a guru course, but rather by a very simple method - by taking a bath in the pool of Vedic knowledge.
What is the symptom of bona fide spiritual master? Everyone wants to become spiritual master. So that is also stated. Sabde pare ca nisnatam. One who has taken complete bath in the ocean of the Vedic literature, sabde pare ca nisnatam. Just like if you take bath, you become refreshed. If you take nice bath, you feel refreshed. Sabde pare ca nisnatam. Without refreshness, one cannot understand this sublime subject matter. And the guru, or the spiritual master, should be refreshed by taking bath in the ocean of Vedic knowledge. And what is the result? Sabde pare ca nisnatam brahmany upasamasrayam. By, after such cleanliness, he has taken shelter of the Supreme Absolute Truth, without any material desires. He has no more any material desires; he's simply interested in Krsna, or the Absolute Truth. These are the symptoms of guru, or spiritual master.
Bhagavad-gita 2.13 -- Pittsburgh, September 8, 1972