The position of the demand curve will shift to the left or right following a change in an underlying determinant of demand.
Increases in demand are shown by a shift to the right in the demand curve. This could be caused by a number of factors, including a rise in income, a rise in the price of a substitute or a fall in the price of a complement.
Decreases in demand
Conversely, demand can decrease and cause a shift to the left of the demand curve for a number of reasons, including a fall in income, assuming a good is a normal good, a fall in the price of a substitute and a rise in the price of a complement.