For me, it’s an ongoing process. I used to obsessively re-live the pain of past experiences and live in fear of future events that never happen.
Eckhart Tolle’s “A New Earth” and “The Power of Now” are books that I read and use for meditation. It helps to remember that anything other than this moment is not reality. They are just thoughts generated by the mind that result in negative emotional responses.
The 12 Steps of Alcoholics Anonymous also bring the focus back to the present moment. They helped me identify the root causes of my negative mental state (it used to be like a very noisy black cloud). I have forgiven myself and others for things that happened in the past. I am also able to deal with fear of the future by having faith that everything will be okay.
I believe that it is impossible for me to ever reach that ideal state of always living in the moment. I accept that there will be times when I will be reminded of my past mistakes and feel guilty. And I accept that there are things in the future that will scare me. In addition, I have many great memories & exciting future possibilities that I like to think & talk about.
After a year of AA and spiritual growth, I can honestly say that I am at peace most of the time. It's an incredible feeling! We can change the way we think but it takes quite a bit of work and ongoing practice.