Live in the Moment
One key to having a healthy mind is to live as much as you can in the moment. Think about what you're doing right now. Don't worrying about the mistakes you made yesterday or the headaches that await you tomorrow. That actually helps reduce the noise in the system.

When you are aroused by stress, you have a very narrow functioning cognitive ability: run, fight, or die. Good for survival but that acute function actually shortens the telomeres on your chromosomes and contributes to memory problems. In the modern age, more stress means the inability to concentrate, and that has been shown to contribute to a shrinking of the prefrontal cortex.

Living in the moment is hard to do, but it is a behavior you can learn with practice, similar to the strategy of thinking about thinking. Example: When you are playing with your kids and letting tomorrow's workday weigh on you, force yourself to concentrate on Candyland, making it a great experience for your kids rather than a distant one for you. It takes some time and effort, but in the end, the act of living in the moment rewards not only you but the people around you.

Source: Dr. Michael Roizen

This is good advice. Although it is not the easiest to do, it is good to do! It's not good to be continually stressed out about things that have happened in the past and are over with.