I can tell you one easy way.....this was taught to me by my AA sponsor many years ago. I was dwelling on the past....and trying to live in the future. Neither is productive, neither has any purpose. I was told to sit in my chair....so I did that. Then I was told to feel how my ass felt in the chair. So I did that. It was amazing to see that it was just not possible to think of anything while I was thinking of how my ass felt in that chair. From then on, every time I caught myself doing either of the two fore mentioned non-productive activities, I would think of how my ass felt in that chair.