Just begin again.
This is one of the most elusive pieces of advice you will ever hear. But it's also one of the most powerful.
Beginning again is a conscious act, a decision that takes place in real time, in the present. The hard part is to do it without disappointment or self-judgment of how things could have been or will be. To simply drop the past and enter this moment.
It's a guaranteed return to the present moment, a way to remain free of thought of past and future, at least for a little while. And it's available to us 24/7. We literally have hundreds of opportunities every day to make the conscious decision to start over. We just have to remember to do so.
When you feel frustrated by something -- by traffic, by a conversation you're having, by any one of the million annoyances life throws at us each day -- you can break this trance at any point, simply by noticing the frustration or self-judgement, almost as a neutral onlooker, and not as "you."
Starting from scratch can be an ethical choice, too -- if you think about it, it's the substructure of forgiveness. The only real way to forgive someone -- or yourself -- is to restart the clock in the present. That's what forgiveness is, if it's real forgiveness.
Consciously starting again is a practice. At first it will be slippery, as you'll still be caught up in thought and carried away by your stories. But with practice and commitment, you can begin to see how valuable it is to snap back to the present moment.