It's hard to be the one who looks professional in those circumstances. Do it anyway. It pays off because students, parents, and administrators notice and respect you for it. Avoid provocative, tight, or skimpy clothing at school. This is true for male teachers as well as female.
Guys have it easier than ladies here.
A nice pair of pants, button-front shirt, and tie CAN'T go wrong. A nice sweater works too. Jackets are optional but look great for conferences, open houses, and meetings. The toughest rule for guys is to have a nice pair of shoes and a good belt . Great clothes with cheap or dirty accessories just won't work.