Your drishti, quite simply put, is your gaze, or where you look.
When you focus your eyes on a fixed, non-moving, single point, your attention naturally follows, making it easier to concentrate (during meditation) or balance (during yoga). Your drishti will help you block out distraction, so you can draw your awareness inward.
When using your drishti, don't squint or strain your eyes - the muscles on your face should be relaxed and the gaze should be soft.
In yoga, while your drishti might help you stay up in Crow pose, it can also be used to deepen your stretch, as in twisting poses like Bound Squat - your drishti can help motivate you to move further into a pose. It can also help you to hold poses for a longer amount of time.
Yoga poses have specific drishti points that are used. In Ashtanga Yoga there are 8. Want to hear more about them? Then
Nasagrai Drishti: gaze at the tip of the nose, as used in upward facing dog and standing forward fold poses.
Angusta Ma Dyai Drishti: gaze at the thumbs, as used in warrior I.
Nabi Chakra Drishti: gaze at the navel, as used in downward facing dog.
Pahayoragrai Drishti: gaze at the toes, as used in hand to toe pose and most seated forward bends.
Hastagrai Drishti: gaze at the hands, as used in triangle and warrior II.
Parsva Drishti: gaze to the side, as used in seated spinal twists.
Urdhva Drishti: gaze upwards, as used in warrior angle, balancing half moon, and prayer twist.
Naitrayohmadya or Broomadhya Drishti: gaze at the third eye or forehead, as used in fish, upward forward fold, and reverse warrior II.