If you were dreaming of wearing formal dress clothes, it means you have an important function coming up. This event could be related to your job, or a big social event. The wearing of formal dress clothes usually signify importance.
This could also be a call for you to revamp your wardrobe and dress formally. You are what you present to the world and people will take you for who you portray to be. If you dress like a hippy, you communicate the message that you are one and people will treat you as such.