Interviews are your chance to let the employer know you are the right person for the job so you must make the best impression that you can.

On the day make sure you are prepared ...even get your things ready the night before if this helps. Sort out what you will be wearing.

You should always be clean and smart when you go for an interview. Even if the interview is very informal you should still make the effort. The employer will be making decisions based on that 'first impression'.