Purify the mind first through the practice of Yama, Niyama and then take to the practice of Dharana. Concentration without purity is of no use. There are some occultists who have concentration. But they have no good character. That is the reason why they do not make any progress in the spiritual line.
Kama, Krodha, Raga and Dvesha: desire, anger, attachment, and hatred
Susumna Nadi is three Nadis in one, one inside the other. See the cross section below to have an idea of its configuration. Brahma Nadi is the central channel, around which is the Vajra Nadi, around which is the Chitra Nadi. Kundali power travels along Brahma Nadi. This three-channel cluster runs along the central canal of the spinal cord.
Tirumular says, "I witnessed the everlasting Bliss light and the Lord's sacred dance on the Mountain hall (Silayaar potu). The Nadi flows like the cascades of celestial waterfall from the mountain peaks of the head. The Kundalini Devi is the lass of astral land. She rises from the Muladhara chakra. Wake him up to meet her. I vow on Para Nandi that he will remain young for ever." Let Kundalini get up and rise from Muladhara through the vertebral column, hold it like a stork at the dam's sluice gate and sit in tranquillity and oneness of thought; you will live forever. Time and Life will remain together when one practices Pranayama properly. Practice Pranayama in silence; silent thoughts are a treasure trove; open mouth (talking) leads to dispersal of breath; closed mouth (silence) takes you to the lunar plane; If the gates do not open, it (breath) turns back in timidity. Breath control helps one lead a long life in a body with two doors and seven windows. Two doors = two nostrils. Seven windows = two ears, two eyes, mouth, anus and genital. If five of ten Vayus (breaths) of the body exit, what goodness does it serve? Waking and praying do not help. Only breath control will restrain the monkey of a mind. Dharana is retrograde involution of body's five senses in five elements, latter in five cognitive internal organs, the latter in tanmatras, and the latter in the Uncreated Being. That is the way to practice Dharana in stages.