Even at the most dressed-down workplaces, there is a line between office casual and college bum. It's time to put away your ironic T-shirts, hoodies and flip-flops and invest in some clothes that say, "I'm not the pizza guy."
Every office has its own definition of appropriate dress. Pay attention to what other people are wearing when you go in for an interview. If you don't remember, you can call the human resources representative at your company and get his or her opinion. You certainly don't want to appear too casual, but you can overdo it the other way as well. You don't want to hear, "Hey, who's the guy in the tux?"
Ladies should avoid wearing anything too revealing or sexy. Dress to flatter, not titillate. Unfortunately, this kind of thing does make a difference: There have been actual studies that show that women who dress provocatively at work are less likely to receive raises and promotions [Source: Lorenz].