Dress professionally. Harry Wong, a genius when it comes to teacher education, has written chapters on the subject. How you dress influences how you are perceived. How you are perceived influences how you are treated. If you are fresh out of college and are worried about being seen as a professional, dress the part! If you wear jeans, t-shirts and tennis shoes to work, you will probably be treated much differently than someone who puts some thought into their clothing.
At our school we have ‘dress-down’ Fridays where staff can wear jeans and a school shirt. I wore a loose T-shirt with our logo on it and one of the boys said, “Are you in your pajamas?” (I won’t be wearing that again.)
Dress reasonably (and I’ll go into that later), but dress professionally.