Whether you work at a gym or independently, fitness instructors must learn to promote themselves to grow their client base. This question assumes you may not have formal sales training but you have learned through your work experience. Here is an example of how to approach this:

"My previous work experience in retail taught me about sales. I learned how to talk with customers and understand their needs. Mostly I learned to listen. When I talk about the services I offer as a fitness instructor I make sure to find out what the client is looking for and explain how I can help them reach their goals. I've learned to share how my skills will benefit them, and how to get them to commit to working with me long term by selling sessions in packages."