Read the job duties thoroughly and prepare accordingly. Just be yourself. They will mostly ask situational questions. Gave mine today, waiting for reply.
Know more about current trends
know more about technology
Comfortable with talking to your clients
Good communication skills
You will be near and presentable
Be very specific about work life balance, many of the jobs do not allow for weekends off...ever.
Be relaxed and be yourself, but be professional at the same time. Staff are often picked based on how well their personality fits with the rest of the team rather than experience. If you have the chance, go into your town's Best Buy and try and pick up the feel of the staff before your interview.
General customer service answer
You're not expected to know a single thing about electronics as long as you can show yourself as a positive personality.
Positive attitude and show great interest in assisting potential clients and be a team player.
Just be yourself and be honest.
Practice situational job situations