By adding friends, both of you can take cards from one another into battle for easier wins. Try to add people that have top tier cards or at least a two-star card. You are able to use a friend's card in battle every ten minutes. Collect as many cards as possible. There is no limit to the number of cards you can collect. You can then decide which of them to level up. One star cards should be sacrificed to boost other cards. Try to increase out the hit points and attack points with the remaining cards. It is better to have many average cards than a single superior card. As you make progress and collect three-star cards, prioritize them for enhancement. Update your cards every five battles as you get new cards. Sacrifice them if they become outclassed by more powerful cards.