Remember, a good interview is one where the interviewer doesn't have to speak much. So research the position and impress them with your knowledge about the job if you can.
It is also important to ask them questions about the job, a good interviewee will demonstrate that they are keen to learn about the job that they are applying for rather than simply sitting there and nodding politely.
With Customer service, it is useful to have experience working with the public. Being aware of customers expectations and the abiltiy to deliver the service that the customer is paying for is vital,
Customer service work is about adapting to each persons individual needs and wants and being able to identify how you can help the individual.
The ability to think fast on your feet and solve problems is important.
The basics like being presentable, polite and well groomed are important if you are dealing face to face with customers.
Customers appreciate honesty. If you dont know the answer to something, customers prefer honesty - so dont tell them what you think that they want to hear if it is not the truth, never be afraid to ask a superior for assistance.
Good luck