If you are currently employed, your reason for leaving will be valuable information for the interviewer to uncover. A careful hiring authority will be sure that they can fulfill your career needs before extending a job offer. The most common reasons for someone to quit their job include feeling a lack of autonomy, lack of recognition, little respect, few opportunities for growth, and being underpaid.
When explaining your reasons for moving on, you mustn't bash your employer or speak poorly of your coworkers. Be less emotional and more factual, keeping your answer to the point. Explain, in a positive tone, what you hope to gain in your next position.