As a teacher, one of the first things you should do, on the very first day with your students, is to establish basic rules and expectations.
(the first things; should do; you) (one of the first things; is; to establish basic rules and expectations; T:on the very first day with your students)
the first things one of the first things
should do is
you
to establish basic rules and expectations T:on the very first day with your students