Answer:
The demand curve can shift either to the right or left. A rightward shift increase the quantity demanded at every price level, while a leftward shift decreases the quantity demanded at every price level.
consumer income increases ⇒ rightward shift
number of potential consumers increase ⇒ rightward shift
price of substitutes goods increases ⇒ rightward shift
price of complementary goods decrease ⇒ rightward shift
consumers expect a price increase in the future ⇒ rightward shift
