I always go to my job interviews dressed as professional as possible. That means a suit, preferably black or blue, crisp white shirt, tie (nothing crazy, the simpler the better) and shined shoes. Doesn't matter if the environment ends up being casual, you want to look like you care and are taking the interview seriously. When I use to interview people, I've turned away guys for simply not wearing a tie. They may have had in a nice suit, clean shaven, etc, but no tie, no interview.
Obviously make sure that you've shaved your head that morning so that it's clean. If you have a beard, make sure it's trimmed and cleaned up. If it's stubbly, shave it off and go to the interview clean shaven. I've had to do that...I went for a job interview and had to have my bead and just kept the goatee because the area around the cheeks had not grown out yet. I grew out the beard once I got the job.
You want to make the best first impression on your job interview and that means looking as professional as you can.