Interviews are not entirely about topics directly related to the position for which you're being considered. The employer wants to get a sense of who you are and whether you'll make a loyal, hardworking employee. From the employer's perspective, if you're the kind of person who's interested and engaged in a variety of activities outside of work, you have the capacity to engage in business projects in a similar fashion. If the interviewer asks you about your interests and hobbies, be prepared to impress him with your answer.
Brainstorm your interests and hobbies before you go to the interview. List the activities that you regularly participate in outside of work and a make few notes to help you effectively talk about the hobby at the interview.
Mention group hobbies rather than individual pastimes if you can. For a job interview, group hobbies show that you work well with other people.
Tell the interviewer how long you've been involved in the hobby. If you have a consistent history with that subject, it shows that you care about building long-term relationships and honoring commitments.
Discuss any leadership positions that you've held related to your hobbies. For example, you might be a part of a community organization that provides assistance for elderly people.
Describe any connections you see between your interests and hobbies, and the position for which you're interviewing. If the skills you demonstrate outside of work are relevant to your prospective job, make the connection for the interviewer.