I use the Serenity Prayer:
God, grant me the serenity to accept the things I cannot change,
Courage to change the things I can,
And wisdom to know the difference.
I don’t believe in the common notion of God, so I usually substitute the word universe instead. In any event, the prayer reminds me to look at events and situations in a way I can handle. Most of the time, I find that I need to practice acceptance (a very different thing than resignation, I have discovered) over many things that trouble me.
Though it may not be this way for most people, for me, I have found I have little control over things I cannot change. It behooves me to accept them and move on.
Again, for me, I have found that what I can change is me. When I am disturbed, I find that the cause of the disturbance is inside me. I have to look and change what I can about me.
Where I have the most difficulty at times is the third line of the prayer. I often lack the wisdom that shows me the difference between what I cannot change and what I can. I’m working on that.