You can summon a special card from the "Summon" menu by tapping the chest icon with dragon head on the bottom bar. Scroll down under the "Gold Summon card" until you get to the free summon. This can be done once per day. By adding as many followers as possible you can earn Interact points. Once you have 200 interact points, you can trade them for a free card. Change your leader card based on what you need from it. For example, choose as a leader a card that gives your troops some sort of bonus, such as attack power. Only enhance your best cards, but keep each element balanced. Evolve your cards as soon as you are allowed to. Focus on the cards that you will actually use in battle for awhile. Use the cards saved in your card box to enhance or evolve first. When you have to, sell your extra cards. Enhance monsters one card at a time for a better chance of success compared to using multiple cards. Although it is more time consuming, it is cheaper. When you get 5 gems, spend them on a Golden Summon from the card summon box. That will give you a premium card that can greatly enhance your troops.