First of all, before you have your interview (and maybe even before you submit your application or resume), RESEARCH the company. If you really want a good change of pace from your current employment, look into the job or career you are seeking. If you know more about the employer and the company, not only will you know if trying to get a job there is going to work for you but, you will also have a foot in the door so to say. Employers love when you actually know what you are talking about when it comes to their business. Look into what they offer, what kind of work is involved, what kind of atmosphere will be surrounding you. Find out as much as you can about the company so you have an honest answer to this question when asked.
As you are researching this job, find out what they do and if you are skilled and able to work in this area. If you are not, you may want to re-think wanting the position in the first place. If you are, sell it!!!! Let the employer know what skills you have that match the job you are seeking. Try to tell them before they ask. This is a perfect way to answer your question! If you are able to do the work they need you to do, without extensive training, your prospective employer will be thrilled! Your skills in this area do not necessarily have to be work related; they could be situations in life that you have learned these skills.
Employers do not want someone that they will spend time and energy on who are just going to leave the position in a short time. As you are researching this employer and company, make sure this employment works well with your future goals in life. If it does, explain to your prospective employer why it does. Knowing that you will most likely be around for a while makes you more likely to get the position.