Show Up Late and/or Disheveled
This may seem unnecessary to mention, but it's one of the most important parts of the interview process. Showing up late, smelling like smoke, chewing gum or having messy hair/clothes can all give impressions of being disorganized, untrustworthy, irresponsible and incompetent. Keep in mind that you're not the only person being interviewed, so little things like showing up on time might not have tremendous upside, but showing up late will make you stand out - in a bad way.