Talking negative things about your previous employer or the job position is a bad interview manner. So, make sure you list out the reasons that are fair enough and in no way related to the attitude of your employer. A few common reasons that are considered as valid can be:

☛ Work in an advanced environment

☛ Further education

☛ Bigger concern with desired career growth

☛ Getting a senior position

☛ Salary increment

☛ Contract expiry or termination