If you stay active and help your guild your cards will keep improving.
Earn Free Coins
When you insert your friends referral code and start the App both you and he can get 1rare card and 10,000 coins.
Free Good Card
Convert your Stat points into Energy until you get at least 100. Doing this will allow you to level up a lot faster and eventually get a LCP Ticket (Legend Card Pack) which will give you a real free chance at getting a very good card.