Although it might seem hard, you can prepare for this kind of question by rehearsing a simple formula. Expect to need to tell a great story about yourself, in around two minutes, and give yourself a short script as a foundation for the conversation.
It can be useful to think about anecdotes from your career that illustrate high points and key accomplishments whilst providing additional interest. Some people like to give themselves more structure, beginning with your current job, skipping back through your professional history, and then forward to what you hope to achieve in your future career.