I generally wear a full suit with a tie and everything....I get to the company, see what others are wearing, if it's smart casual, then when I sit down at the start of the interview I would take off my suit jacket. I then roll up my sleeves a little bit (NEATLY! as in fold it up, not push it up) to try to show that I'm ready to go and ready to get in there and do the work. I don't know if it helps for the interview but at least I feel more comfortable and confident during the interview. (it's more effective during group interviews) Just a thought!