IN MY OPINION,
for those UG students, the first thing is to arouse their interest; the
second thing is to give them several important impression so that they can
have the big picture (or the framework) of the course/knowledge/field.
While, for those PG students, the first thing is to make the knowledge
concrete. Solid and systematic knowledge is the basis of PG training. The
second thing is to expand the students' vision, if possible.
These points are sth just jumped into my mind when I glanced at the topic of
this post. I'm still a student without any teaching experience, so my point
of view only came from my experience of learning. There could be many
answers from other perspectives to this question. Good luck~:)