Much of our mental energy as humans is expended on worry. How do you get rid of it? Clearing your mind won't do; you need to replace your worrisome thoughts with something else. If you want peace, focus on the good.

Resources:

Philippians 4:8-9

Philippians (Baker Exegetical Commentary on the New Testament), Moises Silva

Lectures on Calvinism, Abraham Kuyper (Lecture 4: Art)