A neat professional appearance appropriate to the climate etc. Pilot shirt, clean ironed slacks, polished shoes is fine.
Very important: A knowledge of the operation and aircraft is essential!!!
Very important: 200 hours does not give you the knowledge or experience to tell the interviewer how to run his business or operate his aircraft. Plan carefully and ask sensible questions about your prospective employer and his operation. That usually shows you have carried out research.
Think and plan statements and answers that demonstrate your knowledge of the aviation industry. Safety, legislation, aircraft types, regional demographics of his operation. But don't be a biggot or know it all.
Above all, be relaxed, honest and don't hog the interview!
Good luck!