The tone you set on the first day is usually the one you live with all term, so set it on purpose. Most effective first days strike a balance: warm enough that students feel welcome and safe to participate, and businesslike enough that they take the course seriously. You can be approachable and clearly in charge at the same time.

Let students see a bit of who you are: why you care about this subject, what they can expect from you, and that you want them to succeed. A genuine, human first impression builds trust faster than a list of policies. Students work harder for a teacher they believe is both competent and on their side, and the first day is where that belief begins.