Trataka is a wonderful practice for everyone and especially for the aspirant of meditation. It is actually classified as a cleansing practice in Yoga.
 
What it is?
To put it briefly, Trataka – also called Yogic gazing – is a practice where the gaze is fixed on an object for some time and then that object is visualized clearly with the eyes closed, as an inner image at the eyebrow center.
 
Benefits
Trataka has several benefits which would be helpful to every one and not only mediation aspirants:

Trataka is believed to have a helpful effect in treating and even resolving several eye disorders such as weak eyesight. It improves the internal and external optic function.
It improves concentrative powers and mental resolve.
It helps in disconnecting with the noise and distractions of the external world. This is deeply relaxing.
In yoga, it is said to also develop the “third” eye – the seat of intuition or that associated with “psychic” powers.
 
How it Works?
At the physical level it is said to strengthen the eye muscles by exercising them to focus upon a point. Practicing Trataka on an object such as the candle flame is said to provide a unique ‘balming’ effect to the eyes which help in eye health and in the alleviation of certain eye disorders.

At the pre-meditative level, it is necessary to stall eyeball movement for great benefits and experiences. As we are aware, eyeballs are constantly in motion even while sleeping in the form of REM (Rapid Eye Movement). The aim is to minimize and eventually stall even this minutest of movement. Trataka is a wonderful practice in Yoga to achieve this, as it helps in overcoming this by focusing on a point and then visualizing its after-image with the eyes closed.

Many of the hurdles in our personal lives and even on the path to meditation have to do with our inability to disconnect with the external world at will. In yogic terminology, this would mean the inability to withdraw our senses from the sense objects. Trataka, through the focus on one object, helps to make this disconnect more easily and prepares us to do so at will. This is relevant to almost everyone, but specifically vital for the meditation aspirant.
 
How it is done?
Trataka can be practiced on several objects, but the most popular and effective is trataka on a flame. This is because a flame (such as a candle flame) produces the best after-image that helps in easier visualization of the flame even when eyes are closed. This is the desired effect of Trataka – wherein you can visualize and concentrate on the image even when the eyes are closed.

You should first be seated in a comfortable meditative posture or a squatting position with spine erect. If you have trouble squatting on the mat, you may raise the seating by a few notches.

A candle is placed in a Trataka Stand and the height of the stand is adjusted so that the wick of the flame is at horizontal eye level. The stand is placed at an arm’s length. Trataka is to be practiced with spectacles removed, so people with spectacles may have to adjust the distance between the stand and themselves, so that they observe a clear image of the candle wick without blur.

The focus should on the top end of the wick, as the candle burns. Keep your eyes relaxed while fixing the gaze on the wick. Try not to blink as blinking will interfere in the formation of a clear inner image.

This gaze is kept constant for some time and then eyes closed. With the eyes closed, you should try to observe the inner image of the flame at the eye brow center.

If you don’t see it, don’t be disappointed – you should start seeing it with practice. Keep the eyes closed for as long as you see the inner image. Then re-start.

Detailed instructions of Trataka should be had from your teacher. The Health&Yoga Trataka stand is also accompanied with instructions.

It can be safely said that the practice of Trataka is a powerful practice especially relevant in today’s stressful times and a necessary one for the sincere yoga aspirant. Source