The only method to gain food is by farming. Throughout the game to concentrate on creating more number of farms and feed all your dragons to become dominant in Dragon City. One thing you have to consider about the farms is that your farm will cost you in-game currencies. Hence do proper research and look for crops that harvest in a short time. It will help you to earn more currencies and earn greater rewards. To harvest in a short time consider growing Hot Dragon Chilli and Dragon Bel in your farm.