Positive: Candidates must be positive and excited about the possibility of securing the job. This being said, knowing how to project positivity is sometimes hard to understand. The easiest way is to smile, be courteous and ensure that you speak passionately about how feel you can add value to the company.
Punctuality: It is so important to present yourself early for interview. Turning up late is not going to set a good first impression and will leave the employer with questions about your reliability.
Relevant/Specific Skills: The fact that you have been invited to interview, should already show you that the company sees something in you that they like. They may have seen certain skills in your CV or Application Form that they feel would benefit their organisation.
Professional Appearance: See Interview Preparation section of this course for a full breakdown on this.