Sit in a meditative position with the back and neck naturally straight and place the hands in chin or jnana mudra. Close the eyes.
Gently open the eyes and look forward at a fixed point. Then look up to the point in between the eyebrows. Remain still. This is shambhavi mudra.
Keep looking up in between the eyebrows for as long as you comfortably can, normally a few seconds to start with. You can gradually increase the duration.
Then relax and close the eyes. Repeat the cycle a 3-5 times.