Why do you want to leave your previous job: 

This common interview question is also a tricky one. By asking this question interviewer wants to know that what are the factors that make you think to leave the job and switch to a new one. Now if you will tell them that you are changing the job because of low salary or you get bored because of routine nature of the job then the interviewer will think that you will always find high salary somewhere else and every job become routine job so you may leave this job as well if you will get it. To answer this question you have to do a little research on the company to find something unique about the company so that you can tell this in your answer that "your company is the only place where I can"...  Specify the uniqueness of the company which separates them from other companies.