I started researching positive thinking back in the 90's. I needed to change from my very negative mindset. All my life negativity ruled and I was it's subject. Depression was attached to the negativity and my life was miserable to say the least.
I started watching webinars about positive thinking as well as reading a vast number of books. It wasn't instant change. It took awhile, but my mind started to function positively instead of being on autopilot.
I still have the negative thoughts from time to time, but they are minimal. What a difference!