Depending on the culture of the company and/or stage of interview that you are in, you may get attention over technique issues or HR/personal issues.

For technical issues, just make sure you understand the position and its requirement, as well as some backgrounds of the field.

For HR/personal issues, be prepared with background of the company, its products, etc., as well as your own attitude, preference, views, etc.

Attire must be formal, though you don't necessarily need a jacket, depending on the company/position that you are going for.