How a lesson begins has an enormous influence on what happens subsequently. Having clear and regular routines that are enforced without fail allow you a multitude of benefits, and I've picked out five for your reading pleasure.
There are two kinds of authority you need to have. The first is the one granted to you by your job role. The other (longer-lasting one) is the one you develop as an expert. Learn more about the two here.
You might be responsible for creating the only environment in which they are talked to in a respectful way, as a mature developing adult, on equal par to you in terms of dignity.