Create a room that is perfectly dark.
You might need to tape black plastic over the windows,
And lay a towel at the bottom of the door.
Make it so dark that you can sit with your eyes open
And see not a single chink of light.
Now sit in that darkness, with your eyes open,
And drink in the blackness.
Make friends with darkness,
Reach out into it, and let it soak into you.
Stare with open eyes into the blackness.
Start with an hour.
You can build up to sitting in darkness for many hours, or even days.

Arjuna Ardagh in Leap Before You Look