Anxiety is a feeling of worry, nervousness, or unease, typically about an imminent event or something with an uncertain outcome.
The causes of anxiety can be several from lack of preparation on one's part to complete lack of knowledge of an uncertain future or outcome. Therefore, it is important to practice the dichotomy of control to understand what aspects are in your control versus out of your control.
To begin, figure out if the cause of your anxiety is something you want. Epictetus says, "When I see someone in a state of anxiety, I say, 'What is it that he wants?'" (v. 1, p. 97). If a performer wants not only to perform well, but to "win the approval of his audience" he will need to recognize that: 1) his preparation to perform well is in his control, but 2) how the audience reacts will be out of his control, therefore, to alleviate his anxiety about approval from the audience, he should recognize this is entirely out of his control and therefore, use his energy to focus on what is in his control.
Apply this line of thinking to everything out of your control. In his handbook or Encheiridion, he lists these things as out of our control: "body, property, our reputations, and our official positions."
Body - if you are anxious about getting cancer or having poor health, much of this is out of your control. From cancer to heart disease, a large portion of what happens to our body is beyond our control. But can you eat well and exercise and take care of your body? Absolutely! Do all that you can, that is within your power, to keep your body in good health. But do not let anxiety take over your life, with constant worry. You will soon die, like every human before you. Live well, while you can, but do not succumb to constant worry of the body. Find balance.
How many people who have ate perfectly, exercised without fail, lifted weights and performed cardio every day, but ultimately die in a young age (in their 30s or 40s)? And how many people have neglected these things and have lived to a ripe age in their 80s or 90s?
Property - possessions can be stolen, burned, flooded, swept away with wind or any number of ways. Indeed, attempt to be a good steward of what has been given you. But if you are excessively worried about protecting your property, and when something finally happens to your property, you will be disappointed.
How many people spend all their time and efforts and worries on protecting their property? What beauties have they missed by focusing nearly all their time and effort protecting what is "theirs"?
Reputation - indeed, do all you can to have a good character, but people may still say what they will about you. It is beyond your control.
Career / official positions - sometimes we are compelled to perform a duty or be placed in a position. We must recognize that sometimes what we do for a living is out of our control. We may be drafted as a soldier. We may be called to an assignment at the behest of the company. Indeed, do what you can to ensure your freedom to choose what you do; what position you will hold. But recognize there are times when this is beyond your control.