Demand: This is a good place to begin since most students have experience thinking about market situations from the perspective of a consumer.  Whether students have been exposed to this material previously or not, one of the trickiest parts in this section is the distinction between a change in price and a change in any of the other determinants of demand.  The former, of course, leads to a change in quantity demanded and a movement along the demand curve, while the latter leads to a change in demand and a shift of the entire demand curve.  It is helpful to point out that this distinction is somewhat artificial and is driven by the fact that the demand relationship is being represented graphically in two dimensions.  Depending on the mathematical preparation of the class, it can be very helpful to discuss the demand relationship algebraically without worrying about drawing the diagram.  This allows for multiple right hand side variables in the demand function and no concern about which one leads to which type of change.  For some students this can be an eye-opening observation.