Power steering noise

A month ago I heard an uncomfortable front end noise when I started my car and noticed it was pronounced when I turned my steering wheel left and right. I immediately checked the power steering reservoir and it was empty. I filled it to the full line and it solved my problem. It has been a month now and the problem returned and the reservoir is empty again. Obviously losing fluid slowly. Can you please tell me the order of steps you would take to find my power steering fluid leak problem. Must be losing it as I drive because I see nothing on the ground. Thank you.