This was one of the questions posed by our Learning Design and Technology team at a recent workshop on campus. It's a component of a larger instructional strategy called Backward Design, developed by educators Grant Wiggins and Jay McTighe, Understanding by Design, 2nd. ed. (2005). Backward Design counter-intuitively asserts that when planning a course, a lecture, or any kind of instructional session, begin at the end. In other words, decide in advance what "big ideas" students need to understand and then design the course or session in a way that will achieve these objectives.
Another aspect of backward design involves making the distinction between essential concepts, that is, the core ideas that lead to understanding, versus concepts that have primarily to do with acquiring knowledge or skills, or simply those that are worth being familiar with. Like planetary rings, the latter add to the shape of the whole, but are not the planet itself.
I found the discussion around backward design to be very enlightening as the library considers ways to help students negotiate best research practices and the ever-expanding array of avenues to information that modern technologies make possible. Backward design provides a framework for deciding and then staying focused on what is most important. It is challenging work, but work worth doing -- backward!