A shift of the demand curve to the right means that at every given price, consumers are willing and able to buy a larger quantity of the good than before. This is different from a movement along the demand curve, which is caused by a change in the price of the good itself.
An increase in consumers' income shifts the demand curve for a normal good (such as cocoa) to the right. When consumers earn more, they have greater purchasing power and are willing to buy more cocoa at each price level. This is a change in a non-price determinant of demand, which causes the entire curve to shift.
A rise in the price of cocoa would cause a movement along the existing demand curve (a decrease in quantity demanded), not a shift of the curve. A fall in the quantity demanded of cocoa similarly describes a movement along the curve. A tax on cocoa producers affects the supply side of the market, shifting the supply curve rather than the demand curve.
Other factors that shift the demand curve to the right include an increase in population, a rise in the price of substitute goods, a fall in the price of complementary goods, and a change in consumer tastes in favour of the product.