What's the cliché -- you don't get a second chance to make a first impression? That applies to business, your personal life, and school.
Today, make your students feel welcome and remind them you're glad they came. Stand at the door as they scramble into your class and say a word to each as they cross the threshold. Such a personal greeting not only shows you think of them as individuals, it also helps establish your authority over the class from the moment the kids enter the room. Another side benefit: Potentially disruptive students will be less likely to start class on the wrong foot.
While you're at it, try to find something positive to say to each student every day. You may be the only person who gives them positive feedback, so let the kids know you like them.