Understand that a demand curve shows the relationship between the price of a good and the quantity demanded at those prices.
Recognize that a 'movement along the demand curve' occurs when there is a change in quantity demanded due to a change in the price of the good itself, holding other factors constant.
Identify that a 'shift of the demand curve' happens when factors other than the price of the good change, such as consumer income, preferences, or prices of related goods.
Recall that a decrease in demand means consumers want to buy less of the good at every price, which causes the entire demand curve to shift to the left.
Therefore, a decrease in demand is represented by a leftward shift of the demand curve, not by movements along the curve or a rightward shift.