Set an alarm for 3 minutes.
If you are sitting cross-legged, your pelvis needs to be higher than your knees. Use a block or a cushion. Your back will thank you. Otherwise, sit in a chair and try not to slouch.
Rest your hands on your thighs palms down.
Don't try to stop thinking. Brains think.
Stay still and pay attention.
When the timer is up, get up and carry that attention into the rest of your day.
Extra Credit: Don't tell anyone you did it.