Now working at Microsoft where casual attire can be the norm, it has taken me a while to really internalize this one. I do suggest that you dress one step nicer than the norm. Why? First, dressing nicely makes you feel good and that is a great way to start the day. Secondly, it gives you more confidence and confirms that this is the stand out image that you are trying to communicate. But also because it is observable that you are making an effort, people seem to take you a little more seriously, like they know you come to play and you are likely to be successful. Your appearance is a starting point to making and keeping a good impression.