Briefly describe your professional experience and background. The interviewer is looking to learn about who you are in the context of work. Answering this gives the interviewer insight into how you may fit into the organization. Don't talk about personal information, such as marriage status, children, etc. If you are unsure what information the interviewer is interested in, you could ask, "Are there any areas in particular you'd like to know about?"
Choose something that is not a major flaw or negative characteristic - you don't want to shock the interviewer or make them think you are not a good candidate for the job. Most importantly, don't just say something negative about yourself and leave it at that - turn it into a positive! Describe how you were able to overcome this weakness and a positive way the situation turned out. Show that you have grown as a person, and how that slightly negative characteristic is now a positive attribute that you can bring to this new position. Whenever possible, use specific situations from your previous job to illustrate your point.
This is not an opportunity to brag. Instead, you need to describe why you are the best person for the job. Give a specific example of your strength, what it has helped you accomplish in past work roles, and how it will be beneficial to your performance if you get this job.
Bottom line, the interviewer wants to know that you want to work for them. They don't want to hear that you plan on going to another company or field of work. Even if you do plan on keeping your options open, this may turn the interviewer off. Instead, focus your answer on new skills you hope to learn and master, and how you plan to use them in order to benefit the business' goals.
Be sure to give specific examples from previous jobs, such saving the company money, helping increase profits, completing an important project, etc. Try to use numbers to quantify your answer whenever possible. This gives the interviewer a better understanding of this accomplishment. If you just graduated from college, describe an accomplishment from your school work, part-time job, internship or extra - curricular activities.
This is where your research on the company will be helpful. Perhaps they are innovative in a specific field and that is what makes you want to join the team? What are their goals, and how can your skills and past experiences help achieve them? Give specific reasons, don't speak in generalities.