This is a broad question. Focus on successful client relationships you've had or still have. If you've done freelancing, you'll have plenty of client relationships to use as examples. Explain why they are successful relationships and talk about how you established the relationship and how you nurture it. Discuss communication, working through client issues, and how you cultivate repeat business. Note that this shouldn't be confused with the way you interface with the subjects you are photographing (unless they are the one and the same).

Establishing a solid client relationship is critical to maintaining business and producing outstanding work. I like to spend a lot of time getting to know a client and understanding their expectations. Then I can capture photos that will help them succeed in their goals. I stay in touch with updates on their project and maintain clear and open communication about what is and isn't working with my deliverables. Once I'm familiar with their goals and needs, I can offer other solutions they may not have considered.