What they want to know is what you have learnt about yourself in the process of looking for a new job, and what you are hoping to gain by moving companies.
What They Don't Want To Hear
They don't want to hear you slagging off your boss, company, products, colleagues or focusing on the very negative aspects.
What They Do Want To Hear
They do want to hear you focusing on the benefits of a move and what you are looking to get out of a move. Make it very positive. Focus on the benefits, opportunities and development.
Good Luck!