The key to get throught the interview is to speak well, and confidently while being exceptionally clear and thorough in your speech... but make sure you speak something with sense also.
The main questions that you will be asked on will start from your personal details, such as where you schooled, your educational attainments, your personal hobbies and interests, etc. and then vary into the field on which this call centre is operating in. FOr example if its a call centre for pharmaceuticlas, then they might ask you some questions related to that field, some tricky ones, so MAKE SURE that you go through all neccessary information.(Remember to sort out details about yourself before you say them, such as your hobbies and interests, coz they tend to measure your psychological levels through this too, coz attitude matters alot in a call center job)
Another part of a call center interview is that you get a real type call, and you will have to handle it, and depending on how well you did it, you will score your marks from the interviewers.
At all times, be formal and clear in your speech while being exceptionally confident with what you speak, dont hesitate, and think well before you speak too...
Good luck, and remember, its not gona be difficult, just take it into your mind, and put your best foot forward.