In preparation for an interview, come ready to discuss your portfolio at length as well as your design process and what design software you are familiar with. Graphic design positions can be very specific to the company so make sure you brush up on the company's current design style and are ready to explain how your style and experience will mesh.
Why do you want this position?
Obviously, do not answer with the words "money" in it or anything like that. Answer it in a fashion that would make you stand out from the crowd and make you different. Talk about something specific about that company if you can because that will likely get you bonus points. Know as much as you can about the company for this question. Like how your skills will suit the mission and vision of the company and how you think you can improve the company with what you see with them. I think Matrikon likes team players, so make sure it's a company oriented answer, even though it's about you.