I am amazed at how often candidates will come to an interview late and never acknowledge the fact. This is one sure way to disqualify yourself from consideration. Casual work environments are becoming more and more common. Some of my clients have adjusted their dress code to allow their employees to wear jeans and T-shirts to work each day. This does not mean that you should come to the interview dressed this casually.
Sweat pants are never preferred attire for an interview.
Dress to the standard of the position or industry - at least one step dressier than you would wear to work. Allow yourself enough time to get ready for the interview. Never smoke or chew gum during the interview. Also avoid smoking in your car shortly before the interview. The enclosed space will cause your clothes to absorb the smoke.