Look the part
Your first impression has to be your best impression! Your interviewer will be judging you from the moment you get off the elevator (on time) until the last hand shake, so your outfit is extremely important. Before the interview, do your research on the company you’re interviewing with. Is the dress code relaxed? Do they prefer to see their employees in their best suit? In case this information is unavailable, it definitely doesn’t hurt to ask someone in the HR department.