First impressions mean alot and so you need to go and give the impression that you care enough about getting the job to have dressed smartly, you need to show the person interviewing you that you can pay attention to your own appearance and it matters how you present yourself. It is a matter of respecting the person intervierwing, if you turn up in casual dress they will feel you are not interested enough to make that extra effort to impress.
Wear a smart business suit, (whether male or female) and step forward to shake their hand as you meet them and look direcdtly at them and smile).