One of the bibles of the business world is a book called Dress for Success. This book describes how to dress for the roll of a successful business person and that wardrobe will help you step into that role. In many ways the Dress for Success tells us that how we dress for work is somewhat our "costume" and that putting on that costume of a business professional, you naturally begin to play that role.
Most schools will have a dress code that you will have to abide by as a teacher much as they do for the students. That dress code assures that you will dress in a way that is not dangerous or districting or inappropriate to the job of teaching. And that dress code brings you in line with what the administration expects of the students. But aside from those general guidelines, there is a lot of leverage left to you in your dress so you can express your personality in the "costume" you wear to teach school.
The important thing to remember about the outfits you select is that they do send a message to the students. If you dress very formally, you are telling them to address you respectfully and that you are very much the adult here and they are not. Even if students don’t know they are getting your message, they are and even you don’t know you are sending a message, you are. So its a good idea to think about what message your outfits are sending and how you might customize your wardrobe so the students understand who you are and what your expectations are of them just from how you present yourself to them in class.
One big message to send with your costume is, "I am the teacher and you are the students here." This is not a message of superiority. It is a message of distance. First of all, be aware that this distance between you and the youth socially is necessary and must be part of your approach to your job if you want to be success long term. The classroom is no place for a midlife crisis. Even if you like dressing in a stylish or youthful way outside of class, in class dress like an adult and in a formal enough way that your clothing makes a clear demarcation between you and them.
This distinction actually makes your students feel more at ease with you. Students get uncomfortable when the adults over them try to blend in to youth culture too much and become "with it". Youth people like the authority figures in their lives to be clearly designated and for you to live up to your role as authority figure in your behavior, your language and your wardrobe. So dress for success by having your clothing say, I am the teacher and the students will respond in kind.
Your outfits also have to be practical. Sometimes teaching can become a physical event. You must be prepared to bend down to pick things up and to do some level of low key physical labor even with students in the classroom. This means no tight clothing that restricts your range of motion. It means no short skirts that has you worried about the hemline and your legs all day long and shoes that can keep you going for an entire day of very a very active teaching life.
Just as almost every profession has guidelines for how to dress, these hidden messages and quiet efficiencies you include in your wardrobe selection will go a long way toward making your teaching day successful and comfortable. When your wardrobe is right and you are dressing in the costume of a teacher, you will "become" a teacher and step into that role you were born to play.