It may not be stated in your company policy manual, but if everyone in your office is wearing a suit and tie, don't come to work in sweats. Take your cue from people who have worked there a long time. Be conservative when you start out. Don't let the way you dress detract you from who you are and what you have to offer. Don't be the most dressy or least dressy in your department. Even if your company seems fairly creative and laid back, start out conservative or mainstream, studying the clothing and looks of your coworkers, then adjust your look accordingly.