When asked about why you are moving on from your current position, stick with the facts, be direct, and focus your interview answer on the future, especially if your leaving wasn’t under the best of circumstances.
Always try to put a positive slant on your response; it’s better to give the impression that you’re more motivated by the possibility of new opportunities than by trying to escape a bad situation. In addition, it’s important to avoid bashing your current organization, colleagues or supervisor. An employer is not likely to want to bring on someone who talks negatively about a company.