Sit in a comfortable seated position with crossed legs.
Lengthen your spine and straighten your neck.
If you aren't comfortable sitting,
Simply lie down on your back with your palms facing upwards.
Join the tip of your thumb and index finger to form Gyan Mudra,
Keeping other three fingers straight and the rest of your hands on thighs with palms facing upwards.
Stay here for a few breaths.
Now slowly and deeply pause.
Exhale and at the very end of your outbreath mentally count.
Again,
Inhale,
Pause,
Exhale and then at the end of your outbreath mentally count too.
Keep counting like this at the end of every exhalation until you reach 10.
This time,
You'll start counting backwards from 9,
8,
7,
6 until you reach 1.
There's a rule here that you will follow.
If because of random thoughts,
You even briefly forget which number you're on or hesitate,
Then start over again at 1.
See if you can go all the way up to 10 and back down to 1 without making any mistakes.
Gradually with regular practice,
Increase the counting till 20.