This is an exercise I was taught by a Philosopher/Magician to strengthen your mind and be able to focus on one thing without being bothered by other thoughts.
Every night before going to bed, you light an incense and turn the lights off, then you have to sit on the floor with your legs crossed and your wrists hanging over your knees (if this is too difficult just sit on a chair with you wrists hanging over your knees), don't avoid the pain but accept it and be part of it.
Take a few deep breaths (3 to 4 times inhaling and exhaling slowly).
!The room must be completely dark!
Now you have to focus on the glowing top of the incense, do this for 10 minutes,
every time a thought comes up in your mind you have to close your eyes quickly and open them again focusing on the glowing top of the incense.
After finishing this exercise take a few deep breaths, slowly stand up and turn the lights on.
This is a good exercise while you read the theoretical part of IIH