from Guru, by His Holiness Sri Swami Sivananda Saraswati Maharaj. Swami Sivananda (1887-1963) is one of the most well-known and well-respected Indian Yoga masters and Hatha Yoga teachers of 20th century.
If you find peace in the presence of a Mahatma (great soul), if you are inspired by his speeches, if he is able to clear your doubts, if he is free, from greed, anger, and lust, if he is selfless, loving, and I-less, you can take him as your Guru. He who is able to clear your doubts, he who is sympathetic in your Sadhana, he who does not disturb your beliefs but helps you on from where you are, he in whose very presence you feel spiritually elevated — he is your Guru. Once you choose Your Guru, implicitly follow him. God will guide you through the Guru.
Do not use your reason too much in the selection of your Guru. You will fail if you do so.